My Mom has financial difficulties due to my own daughter. What can I do?

IF your mom's only problem is mobility problems and she has no cognitive issues, mom can do whatever she likes with her money. However, the fact that you say that your mom seems to have difficulty "understanding" why she's short on funds would seem to indicate that mom is no longer able to handle her own affairs.
Some suggestions:
Call Adult Protective Services to investigate for financial abuse of a vulnerable elder. Ask your mom who she wants to have handle her financial affairs; get her to an Eldercare attorney to assign SOME responsible adult as PoA. Get your a referral for a neuropsych evaluation to see to what extent she is competent to handle her own affairs.

Your daughter has rule that you can't interact with her (your daughter?) or your mom? NO ONE who doesn't have guardianship can tell you that you can't interact with your mom.

This type of behavior on the part of your daughter is consider elder abuse. Even if your mother agrees to help financially, your daughter is exploiting her. I would report it to an elder law attorney to see what can be done. Doing nothing is only increasing the problem and eventually someone, like yourself, will have to financially support your mother. Think about it. Your daughter is exploiting your mother.

Everyone seems to think that the Mother can dictate to her adult daughter and set up rules to be followed. I can guarantee they have not lived this scenario. The granddaughter is a narcissist and, the grandmother a co-dependent enabler. And for those of you blaming the mother for the daughter’s behavior-you need to rethink that. The mother’s not the one enabling and adult; the grandmother is. The daughter no doubt stays away from her mother. The granddaughter learned a long time ago that her grandmother can’t/won’t say no to her and; that’s her ticket to exploit her. The grandmother may think she’s helping her granddaughter out of love but, it’s actually co-dependency. If the grandmother actually loved the granddaughter she’s let her grow up and learn to manage her own life. I’m speaking from firsthand experience. It’s particularly scaring if the grandmother might need Medicaid in the future. The mother can talk to the daughter and granddaughter until she is blue in the face and, it won’t make one bit of difference.

My brother was doing this to my mother. I don't think she knew the difference between $20 and $800 at that point. I took her to her bank. Closed her account. Then I took her to my bank, opened a new account in her name but I was the signer. From then on I paid all of her bills. It worked like a charm and I was able to keep her in her home until 2 weeks before she died at 90. If your mom is lucid, explain that this is the only way she can keep her home. I think as they get older, they loose the ability to say no. It might be a relief to your mother to be taken out of that spot!

minnesota25: Your mother is an enabler. THIS MUST CEASE NOW! Good grief, your mother is going to lose her house over enabling her granddaughter? That tells me that your mother's mind is going downhill.

You could have your mother make you or another family member POA of her accounts and require that any expenditures go through the POA. You could also have the county aging services investigate.

I agree with the above poster that you need to get this stopped. If your mom cannot afford her house any more and cannot afford to private pay for independent or assisted living and has to go into a nursing home on Medicaid, there will be issues with the gifting of money during the 5 year look back period.
Is your mom able to understand that she cannot afford to be giving your daughter money? If not, you have a great case to become her guardian or get financial power of attorney to protect her assets.

Mm. Even if your daughter, at approaching 30, is an independent adult would you not feel some residual responsibility for her behaviour?

My children are all around that age. I don't pretend that I like everything they do, or every choice they make, of course not. But I can't imagine taking their exploitation of a grandparent lying down, if they were ever to do such a thing.

I'm not suggesting that the OP should prevent the granddaughter seeing the grandmother at all, and I agree that the older lady has a perfect right to see whom she pleases and to do as she pleases with her own money, assuming that she is competent. But the OP describes herself as her mother's main carer for five years. That must count for something. Not least, it implies the OP's gradual assumption of responsibility for her mother's welfare over a significant period of time. To suggest that she can safely sit back and say oh woe is me but what can I do... I don't think it's a good bet. I think she would be implicated in the financial abuse if she allows it to continue unchallenged.

So challenge it. Loudly.

As an RN and attorney who deals with elder law matters daily I suggest family mediation. You, your daughter, and a trained and experienced mediator may be able to reach an agreement, which should be put in writing. If it is drafted by a knowledgeable lawyer-mediator it is enforceable as a contract. Trying to use the law with a "willing victim" doesn't always work so well. They tell authorities everything is fine. Search eldercare mediators in your state for referrals to competent mediators. Otherwise, you need to let your mother know that she will likely lose her home if nothing changes.

Churchmouse, we weren't able to deal with it in any useful way really. My in-laws went through all their considerable money enabling grandson. We always thought it was my MIL who wouldn't say no to grandson but after her death in 2013 it became clear who the real culprit was-grandpa! He would complain about being short of money and grandson but refused to actually take any steps to stop it and would go behind our backs to keep the handouts going. Those two were the perfect storm.