Grounded at 21

So my mom just threatened to ground me at 21 because I pissed her off. What happened was I asked if I could see a movie with my friend tonight and she didn’t like that I had plans of going out on her day off from work. And when she said no I tried explaining to her that I’d only be out for 3 hours at night and I’d spend the whole day at home and she viewed that as me being disrespectful and argumentative. She started yelling at me and when I asked her nicely to stop yelling cause it’s so hard to talk to her and have a conversation with her she got even more mad and told me she can do whatever she wants cause I’m her kid. She’s right I am her kid but I’m also 21 and not 10 years old and she still can’t talk to me normally. I get it’s her house her rules but I feel like I’m being suffocated