Sounds like your mom has had a life time of issues. There’s probably not much you can do about that, unless when you come back, she is willing to go to family counseling with you.
Because you know her tendencies, you should just not let her “handle” things anymore. You don’t have to get into an argument with her or yell at her or even feel crappy about it yourself. That wouldn’t serve to help either one of you. Just know her nature and work around it as much as possible. Make it easy on yourself by never putting mom into a situation in which she is likely to disappoint you in a big way (like making her responsible for mailing things, bringing stuff to the party, making the turkey for Thanksgiving or any other situation where you need her to do something and have it be done on time) She’ll probably do all sorts of annoying little things to disappoint you, but if you expect it ahead of time you can work around it and talk yourself into not getting mad at her (and not beating yourself up about it either, you don’t need to feel like shit for something that you can’t change).
I think that old Serenity Prayer thing would work well in this case. I think @yarnlady has a copy of it somewhere.
Is she coming to your wedding? If so, just don’t put her in charge of anything. Just make sure that someone is there to take care of her and make her feel “special” even though it’s your day. That person who is assigned to take care of her, should also make sure that mom doesn’t get in your way and cause you any problems. It’s almost like you need to get an adult babysitter for her, but she needs to think that the caretaker is just someone being nice to her (not that this person is really there to keep mom busy and out of your hair).
One of my friends had a difficult and annoying mom. I often volunteered myself to be put in the role of the temporary “caretaker”. She loved it because I gave her lots of attention (mostly just agreeing with her and letting her yammer on endlessly), but kept her out of the fray when my friend needed to get things done without her mom interfering and interrupting.