MIL keeps saying "I'm not a child". How would you reply?

I believe in utter honesty in these instances. I believe the correct response is "We are aware you aren't a child, and we understand that it is difficult when people remind you of things you are already aware of, but the truth is that since your stroke there have been some changes. We aren't aware how aware of these changes you are (list them; perhaps in fact keep a diary of them). Because we see these things being missed we are tending right now to give you more reminders than you likely need. We are so sorry, but we are trying, honestly to protect you. We know that it may feel like a loss of control, but the truth is we are concerned and we won't always do it "right". But you need to understand also that right now you are not up to full speed; we can't deny that to you." Again, give her real instances.
If at the end of all this, you cannot "talk it out" a bit, then perhaps there is no real good answer. That's so often the case in life. You do the best you can, and on your go.

Your MIL is feeling her life and independence slipping away. It has to be terrifying for her. Imagine it happening to us, I have. She needs reassurance and to be told “you’re correct, you’re absolutely not a child. How can we work together to best solve this ........
? Whatever the current issue is, she needs to feel support and help finding a way forward. It’s not on you to fix everything, you’ll go nuts trying, but make her a part of finding answers

It's likely your MIL is suffering from cognitive decline now, or dementia, after her stroke. Is she living alone? That will likely need to change and you will need to have a plan in place as she continues to forget her medications and other important things in general. She may improve, and then again, she may continue to decline. My mother has continued to decline after a stroke she had in 2018 and is now trying to call her dead sisters on the phone. Sigh.

I think I'd say to her in response to "I'm not a child", of course not mom, I'm just here to help you sort out some loose ends now that you're recuperating from a serious illness. Just till you get back on your feet. Something along those lines. While she's not a child, her mind is likely going down that road to where she IS becoming childlike and realizes it. Nobody wants to face that eventuality!

Wishing you the best of luck with a tough situation.

" I understand this is a difficult time for you mom. You had a medical issue and you need time to heal. Please let us assist you so that you have the time and energy to focus on your healing."

My Mom says this also. I try to give her simple choices so she has the feeling of some control again. I just did this actually. Do you want to visit the bathroom now or in 5 minutes? She usually picks the latter. Tonight she surprised with 10 minutes, lol. I said, ok, you’re the boss. I do this with medication also. Do you want to take your pills with water or applesauce? The tasks always get done but she makes the choices. Good luck.

Such an important question... it comes down to dignity in conversations with our seniors or anyone in this situation needing care... Utmost Respect for the fact that they are NOT used to asking for help in the first place. Helping a person becomes more of a plan to help themselves. Asking great questions is the first plan of action and in a way that empowers them to CHOOSE who, how and what needs to be planned. "Mom, I know this is not the best situation and I cant imagine how you must be feeling. I want to help and I also know that is not something you are used to having to deal with but I am here for you like you have been there for me. How can I help. (Listen!) Let her talk it out. If you get push back share that you have some ideas you would Like her to Consider when she has time to ponder all the situation is bringing to her table so to speak. If she is emotional or just not able to deal then excuse yourself to give her some space.. come back with a nice cup of lemon tea and re-approach the subject. No One Wants to be Bossed around.. At Any Age.. but especially the population of Seniors who basically Built this Country lol.

lol - while you're thinking "it's for your own good", maybe out loud say something non-argumentative like "Of course. We're just trying to help you out a little.". She obviously needs help but doesn't like it showcasing her shortcomings. Understandable. When I took over some of my mom's things, I told her it would be easier and less stressful for ME to just do it instead of "helping" her do it.

She is just adjusting to the new “norm”, but there will the next thing, then the next, then the next. The aging process is really hard. Fasten your seat beat and keep on loving her.

When talking to her adopt a “we are in this together tone”. answer: “everyone needs help sometimes. Don’t refuse my help, assistance advice, etc. because you feel you need to do everything yourself. Let me help so we can make the best decisions and you and I can learn new ways to keep you safe.”

In my opinion, it is a bad idea for anyone to take on the responsibility of caregiving without having the authority. But first, you and your husband must be on the same page about what you both are and are not willing to do for her. Do not make promises you cannot keep e.g. "We will never put you in a home".

Does your husband have durable power of attorney both medical and financial? If not, then this is a conversation you must have with your MIL. Do not beat around the bush with her. Be direct: "Mother, you are right that we cannot take over your affairs without your permission or understanding your wishes. We've given it a lot of thought and you need an attorney to help you sort through these important decisions. Do you have an attorney you would like to consult?" Then be quiet and see what she says.

Having this conversation demonstrates that you respect her as an adult and are willing to help. It also gives her the power to decide who she wants making decisions for her. An attorney will help her get her important paperwork done i.e. living will, will, DPOA. If she refuses then step away.

When it became clear my in-laws needed help managing their affairs, I insisted that my husband get their authority to help. Fail to plan or plan to fail. She's an adult so treat her like one. Adults plan and her needs will only increase. *She* must be prepared for things to change whether that's bringing in help at home, renovations to the bathroom (raised toilet, grab bars), etc. *She* must understand what is within her financial means and what isn't. And whoever has financial POA can help.

A dear friend of mine who does not have DPOA either medical or financial has been living a 5-year nightmare with her parents who chose a distant cousin to be DPOA. Yet whenever her parents need something, they call her. She's exhausted and I keep telling her to stop driving the 8 hours to get to them because she's not their POA. She won't listen. She keeps expecting things to change. She's given herself an ulcer.