Fallen out with my friend, should I still do her a favor I commited to?

A close friend of mine went to college at the start of the academic year and I stayed at school to attend the sixth form. My friend (friend A) and I have always argued a lot, but now we don't see eachother every day it's harder to make up. We see eachother most weekend and some days after school but she always gets crazy angry when I do anything with my other friends (even when she went to school she'd get jealous of my other friendships, but it's worse now).

Anyway, she's studying photography at college and asked me to model for her coursework project about a month ago, we were fine at the time and I agreed. Since then another friend of mine (friend B) invited me to the cinema with her, and said to invite friend A along. When I asked friend A she said she didn't want to see the film with friend B (even though they used to be good friends) and asked me to see it with her seperately. I said no because I didn't want to pay for a film twice, but that I'd do something seperate with friend A. She then had a strop over text and stopped messaging me for about a week. She was meant to sleep over at my house that Friday but didn't show.

My cinema plans with friend B were made for tomorrow and we invited a coupl other friends along. We were also invited to a group thing after school the same day as we were going to the cinema, so we decided to go to the group thing then go to the cinema that night. Then friend A texted me and said that she needed some practise photos for her project on friday and could I come to her college after school. I didn't want to start another argument so I cancelled my group plans and said I'd meet everyone at the cinema later. Then friend A wanted to stay friday night after the shoot and I told her no because I had cinema plans, but she was still welcome to come if she wished. At this point she sent me a series of log messages about how I no longer make any effortin our friendship and don't text/ call enough. I sent a reply in my defence, and she claimed to be 'too ill and upset' to read my messages.

The next morning (Tuesday) I texted telling her to find another model for friday, and she said that exactly proved her point. I replied I was doing it because if that was her opinion of me I may as well conform to it, and she might better understand that if she bothered reading half my texts. She completely dismissed this and said, "I can't get anyone else, I don't have another friend." and "I'll be at the train sation on friday, and hoping you'll get off".

We haven't spoken since then. Thing is, she used to be really popular, but her irrational mood swings and jealousy led to a lot of arguments and eventually everyone but myself and her boyfriend deserted her. Now she gets jealous and angry about the slightest thing and tries to control everything I do. So should I go to her shoot tomorrow? On the one hand I made a commitment and should stick to it, plus I don't want to lose her friendship forever, but on the flip side I'm still upset by what she's said and don't want to just do what she orders me too.

Sorry for the length of this! Thank you so much if you've read this far! :)