Any tips on what I can do abut my grandmother throwing clothes away?

I’d suggest taking most things out of GM’s area. You can rotate them over two or three weeks, if you want to. That's what we did for MIL when she went to the nursing home. If GM has lots of choices, she is more likely to chuck. She may even find the number of choices is quite hard to handle. And put a 'trash can' with a clean liner where she is likely to use it, to make a nightly sort less horrible.

Is your grandmother just doing some fall cleaning and wanting to get rid of things she no longer needs or uses? Or are the things she's throwing away things that she still wears and uses?
The answer to those questions will make a difference in how you proceed, as if she's just doing some fall cleaning out of things...just let her. But if she's throwing away perfectly good items that she still needs, well that's a different story.
But the bottom line is that if this simple thing of grandma throwing away things is stressing you and your mother out "to tears," my goodness...you ain't seen nothing yet if in fact grandma has some form of dementia. The fun is just beginning.
I'm glad that you and your mother both realize that you're not cut out to be her caregivers. That is huge. So now it's time to get your(or grandmothers)ducks in a row as far as her future care.
Start looking into assisted living facilities in your area where she can be around other folks her age and enjoy the activities they provide. Make sure that this facility also has a memory care unit that she can progress to if and when needed.
But for now, take her to the doctor to rule out a UTI or any other issue that may be causing this current issue.

Sometimes people just want to get rid of stuff they don't need, and as we get older, we don't need so much stuff.

If she has dementia, she may be trying to clear out all the stuff because it's confusing her, she doesn't know what it is, she doesn't know it's hers, etc. Who knows what goes on in their heads?

One thing you could do is organize, organize, organize. Keep clutter around her to a minimum. That might make her feel calmer. I know it does me; I find disorganization and messes uncomfortable. I don't want to be in them, I don't make them, and I don't like to be in others' spaces that are cluttered and messy either.

Also, please stop thinking of "putting her in a home." That phrase has a connotation of consigning her to a bad place. Care facilities today are much nicer than they were yesteryear. Grandma would have activities, outings, friends, and professional caregivers to help her. Think of a care facility as getting all of you the help you need. Go visit some soon.

All memory problems in a 75 year old are serious and do not get better, only worse. With elders who suffer from Alzheimer's/dementia, it's common to be getting rid of things.

Here is a link to a discussion on that very topic:

https://forum.alzheimers.org.uk/threads/mother-is-obsessed-with-throwing-things-away.76597/

Get grandma in to see her PCP and make sure you ask that she be tested for cognitive issues. A MoCA or SLUMS mini cognition test will suffice to see where she falls on a 1-30 rating chart.

Good luck to you

Not everyone has the bandwidth to live with someone with dementia. If in fact that is what is going on here .

Take grandma to the doctor and rule out other things such as UTI, depression etc.

If it is dementia it will only get worse .
Why does grandma live with you ? Does she have funds to pay for assisted living or memory care facility ? Depending on what state you live in Medicaid will pay for that when grandma runs out of funds . More information would be helpful . Come back here after you have seen the doctor .

Your Grandmother needs to go to the doctor. If this is recent change this could be UTI as she is old now for early onset dementia and young for dementia itself. You don't tell us what other symptoms you are observing.

This is your mother's problem. The more you step in the more you enable her to step away and this is not your problem. Your mother needs to start with the doctor and a solid diagnosis. Then your grandmother may or may not need placement, according to what decisions your mother comes to.

I don't know your age, but if you are of majority it is time now to move on and move out and begin your own life, education, job, family, etc. I wish you the very best.

UTIs can cause sudden dementia like symptoms. How long has this been going on?
You will be amazed at how much better she will be after treatment if that is the case. get her tested.
This can be done at an urgent care. Ask that they run a culture to make sure she gets the right antibiotic. UTIs can be fatal.

If this is just happening at night perhaps it’s a form of sundowners.

A dementia diagnosis will be beneficial as you will understand better what you are dealing with but it won’t stop her activities.

If it is dementia, she won’t remember not to do it just because you tell her. Some dementia patients pack a suitcase everyday to “go home”. Some take their clothes off. Some don’t take their clothes off for weeks. Some are not preoccupied with clothing at all. It’s a complex disease.

Your mom is probably afraid and it is very upsetting. I’m sorry you all three are having to deal with this. The sooner you get her to a doctor the better.

Maybe cull through her closets and leave her with enough clothing to last for, say, a week, from wash day to wash day.

Then replace the dirty clothes with clean ones.

I get the not wanting to dumpster dive every night--or maybe you can put a largish trash can in her room for her 'extra clothes?'

Maybe she's feeling overwhelmed by the sheer amount of stuff she has.

My MIL has been throwing things away-totally random items, for about the last 4 months. Luckily the 'kids' do sort her trash and pull out the items that are not garbage. Now she has dementia, she doesn't remember nor care that she's throwing things out.

Personally, I'd take the purge over hoarding!

Agree with others that you need a real dx here. Make sure she gets a real test for memory loss and that she is tested for a UTI (which can mimic dementia). Make sure you have all the very important documents (VIDs).... DPoA, Advanced Medical Directive and Will. Now if grandma is diagnosed with memory loss it may be very difficult to get an attorney to draw those documents up for you. If those documents are already in place and your Grandmom is dx'd with dementia, then the DPoA ( your Mom perchance?) needs to prepare to step up to the bat and start making some hard decisions.
Memory care is not what it was 30 years ago but with the advent of covid, all medical facilities are short staffed. If your Mom can't deal with someone with dementia (and dealing is not an easy thing) then you will need to consider placement or home care (also can be expensive and you will still have to deal with her when the caregivers are not there). Assisted Living and MC are fairly expensive everywhere (think 3-4K per mo. min) and the fees increase with the level of care required. Regardless of where Grandmom is placed, family will have to visit often to advocate for her. In many states, Assisted Living and Memory care do not take Medicaid (should she qualify financially) without a significant prior period of private pay. Under no circumstances, will Medicare, which is a health insurance, pay for custodial care.

So to find out where you are at.... start with getting a full physical and neurological exam. Please let us know how things turn out.

Alexalain909: Take your grandmother to see her primary care physician for cognitive evaluation. Something seems amiss with her throwing clothing away UNLESS she just had too much. Even so, most people (when purging out items) donate to charitable organizations.