I'm well into my mid twenties and sometimes I dream of running away from my controlling mother, who manages to control my life when I don't even live there any more and make my life a living hell, all from "good intentions". Hell was also paved like that.
Unfortunately, having been in this situation, it's not easy just to say, "Mom, you need to back off now, I'm an adult." Mothers meddle no matter what you tell them.
She only controls your life because you let her. Grow a backbone and tell her to back off. Either you're not giving her good enough hints that it upsets you, or she's crap at reading them.
damn, I could have written this (well not the living hell part, but the controlling) . Slowly set some boundaries, so she knows she can't control you anymore.
you just need to be like "mom, this is the way i am going to do stuff and thank you for your suggestions" that may be a good way to say something so you don't hurt her feelings. she may not even know she is still being controlling.
If her intentions are genuinely good, you should be able to explain how the way she is behaving is actually affecting you negatively, and preventing you from being independent and learning to trust your own judgement - that she is teaching you learned helplessness. If she makes all your decisions for you, she is de-skilling you, and you won't learn to be responsible and make your own decisions, and you won't be able to survive in the world after she's gone if she continues like this. If her intentions for you are good, this kind of explanation should make her rethink her behaviour, because she wants the best for you. But try to explain it in a calm, adult way, as if talking to an equal, rather than like a sulky/angry teenager, so that she can trust you and start seeing you as an independent adult.