It seems that some parents have a much harder time than others at adjusting to their children becoming adults, and it sounds like your mom is one of those parents.
I had a similar situation with my mom taking it personally when I didn’t do what she wanted, even if it was an unreasonable request. My siblings got her to stop with them by arguing or yelling at her, but that didn’t seem like a satisfactory solution to me.
I took the approach of being calm, concise, and consistent, and I chose my battles. When she asked me to do something that was burdensome for me, I’d simply say, “I’m sorry, I can’t do that.” Then I’d repeat it in the same calm tone as many times as it took for her to get the idea. Going into details about the reasons would only give her fuel to take it personally, e.g. “you think that going to your best friend’s birthday party is more important than coming to my house and helping me get ready for my dinner party. You must not love me!”
Also, I appreciate you wanting her to tell her that her behavior is unacceptable, but I doubt it will work with her. It sounds like she gets so defensive when you point these things out that she can’t hear what you are saying. What might work better is gradually getting her to realize it for herself. Of course, this approach take a bit longer, but it’s better for everyone in the long run.
Perhaps try to have some responses on hand that acknowledge what she says, but respect your autonomy, such as,
“I will keep that in mind. I’ll really need to think about that more before I make a decision.”
“Thanks for your opinion”
“I don’t know, mom, I guess I’ll just have to see for myself”
“Well, I guess that’s just one of those things that every young woman has to learn for herself from experience”
“Mom, I appreciate your (name removed by moderator)ut, but I really need to do this my own way”
“That’s an interesting idea”
[Of course, tone is everything with expressions like these. If you sounds angry or sarcastic when you say them, they don’t work]