In posts like this a lot of people from non ethnic (minority) backgrounds comment the typical 'move out', 'hit back' etc and whilst it's appreciated that you're trying to help, in certain cultures things like that just are not an option. Those boundaries don't get crossed.
I'm of an African background and I understand where you're coming from. Although I'm probably lucky in the sense that my parent's aren't at all strict with me. I have my curfew and so long as I'm back by then there are no problems.
I honestly think this is the type of situation though where you need to do something. You need to sit and talk with her. Discuss the fact that you're making new friends, reinforce to her that you know the culture and wouldn't be doing nonsense before marriage etc. Try to set up a curfew between the two of you so that at least you can say to her Mum, if I'm not home by ____ I will understand why you're calling me because I'm probably in trouble etc etc. Or agree to text her at certain intervals to show that you're safe etc. It's all about trying to find a compromise and trying to force her to listen.
Unfortunately though if this doesn't work you will probably have to rebel. If she refuses to work with you you can't throw away your social life and friends because of your mother behaving irrationally. If she tries to hit you defend yourself and make sure you speak up. Don't hit her back though. After any altercations give her the silent treatment. Just live your life a bit and eventually she'll have to let go. Hope this at least helps a little bit.