I personally found it very freeing when I realized that my analysis of my mother's "requests" need not include any analysis of whether the request was "reasonable." Some of her requests are FAR from reasonable in an objective sense, some are quite reasonable in an objective sense...and that reasonable quotient is in no way related to our choice of how to handle the request. We simply have to decide if the request is one we are happy to give her, one we could be happy to give her with some adjustments, or one we are not happy to give her. If we aren't willing to give it, it doesn't change anything that it is something others think we should give or that the average person would be willing to give.
POD! One of the things I've learned about my MIL is she is queen of the "foot in the door" technique. She starts with small requests that would be reasonable if we didn't know her history and quickly escalates from there. So if that initial, small request feels hinky to LordL and I, we just say no and redirect. It might make us look harsh to an uniformed observer but we've prevented boundary trampling this way for a few years now. On the other hand, I posted here about my BIL who ok'd a visit by MIL and FIL only to have the invite list grow from 2 to 7 without his consent in under one hour. Part of the process for us was to trust our instincts and not compare the actions of a dysfunctional person with what a "normal" or ideal parent would do.
I just had another run-in with my MIL and fell for her expert use of this technique. What started as a seemingly simple request for DD to participate in a ceremony at her church turned into a weekend long commitment plus a weeknight event beforehand. (And I think there might be a parade in a few weeks... details are fuzzy, despite the questions I've asked.)
All she did was reinforce my boundaries... That'll be the last ceremony DD participates in, no matter how important it is to MIL.
My "punishment" for pointing out that the event had changed significantly from the one we'd agreed to? She didn't tell us that she was going to Old Country for two weeks. Hahahahaha!