She was in the unfortunate position of allegedly being drunk last night as a passenger while her boyfriend was arrested for DWI.
It's really not that unusual for a passenger to be arrested for Pubic Intoxication in that situation. The fact that you are in a car doesn't mean you're not in public. (But I have seen some videos where the passengers initially refuse to get out of the car because "Once I do, you'll arrest me for PI!")
But Wise County law enforcement seems to be pretty understanding in these situations. More often than not, they'll give the passenger a chance to call someone to come pick them up. If they can't find someone, then they'll be arrested.
Edit: Christina's book-in info has her at 100 pounds.