Katydid I understand your frustration. I am a see a problem and go fix it person, so your MIL would drive me nuts, too just on the face of it but I have this sense th a t she knows exactly what she is doing(?). What can you do to take care of you. It's not always easy to let it roll off your back.
Can you divorce yourself from her care? I would think your husband can see this isn't working for you. Can you tell him you need a break and HE
needs to do all her errands.

Honestly my MIL so far has been pretty minimal work,but I often say I have already cared for my elderly parents so he needs to now take care of his mom. I will coach him, but she is his responsibility and his brother's.We have been married 25 years and this has worked. Mind you there were many times it would have been faster and easier to do for her myself, but if that happened then i would own it forever.
Hoped this helped. I am in your corner!