WHAT I"M ABOUT TO TYPE IS ALL CONJECTURE AND IMO BASED ON WHAT I UNDERSTAND TO BE FACT:
I don't think she was in the car accident at all.
I think she got out of her BF's car after arguing, walked back to her apartment, and found that her car was gone/"borrowed" by a party-goer.
I think she flipped out and tried calling her BF over and over again, because having you car stolen trumps being PO'd at your BF and puts things in perspective darn quick. If there was unaccounted for time in here, I think she spent it being angry at the roommates and demanding answers but got none.
I think she couldn't get ahold of her BF as she was heading back outside, still amped up from her argument and full of adrenaline from the latest development, and started looking for her car. I think she called him and called him while walking around with angry "beer muscles" feeling invincible and not watching out for herself properly, finally texting him she was coming over because perhaps she decided that she was going to call a cab to take her there if she didn't find the car within the next couple of minutes.
Then perhaps she found her car just a couple of blocks away with tires blown out, locked, and she realized for the first time that she didn't have her spare key on her (her normal keys having been swiped while she was gone and used to "borrow" her car), OR her wallet to pay for a cab. This would be easy to forget, having run out to look for her car in such a haste; so perhaps she walked back to the apartment to get her spare key (maybe changing while she was there) and called a cab while she was there, knowing her car was undriveable for now, but intending to call someone about it in the morning when she was 100% sober (her dad, a tow company, AAA, whatever).
I think perhaps when they told her it'd be a good 20 minutes before the nearest cab could come I think she decided to walk to the store and meet it there because she was angry, assuming someone at the party had taken her keys and her car, and didn't want to be there any longer than necessary, heading out with a peeved sense of "I'm so over this, I'm outta here!"
I think perhaps at this moment, while she was getting ready to grab her spare key and wallet and head out to the AMPM to meet the cab, something happened to her. Perhaps someone heard her being angry her car was gone. Maybe she ranted that she was going to turn in whoever she found out did it (snitches get stiches, dontchaknow)...
Maybe. IMO. For now.