MOH is my younger sister. Seemed a logical choice at the time but this was also de facto expectation since we were kids. She lives in VA, and myself and my 2 other BMs (friend and FSIL) live in MA, where I will be married. This did not seem an issue at the time since I'm not really asking my maids to do things.
Evidently my mother has some serious baggage from her own experience as MOH for her sister, because in response to that she has decided that only my MOH gets to come dress shopping or have an opinion (I overruled her, but that was an emotional-wreck-mess), and only my MOH gets to do traditional MOH duties like planning a shower or bachelorette (or, apparently, even coming to venue tastings). This is to ensure that my MOH receives proper deference. Obviously, as MOH lives in VA, by my mother's rules I can't have BMs involved in much of anything (I literally got yelled at for bringing my BM to a venue tasting), so I can't have any of the pre-wedding parties. This is something I'd normally be OK with, except that my mother's "this is what happens when you move far away" reeks of her trying to punish me for living where I want to live. Which sucks.
Practically, mother has limited control -- she is paying for 1/3 of the wedding, but I don't believe that would usually entitle her to deciding BM duties(?), and she doesn't live here. However, it's difficult because my mother's protection of MOH is the continuation of years of being told that I am a big sister who constantly ruins MOH's life, which makes it harder to ignore what she's saying. She's made this about something I've been 'trained' to feel guilty about for a long time.