Okay, this is kind of gross. When you are throwing up and you have long hair, you need to pull your hair back away from your head so you don't... well, you can form your own picture.
At times, someone will be so drunk that she will require someone else to hold her hair while she vomits. (That person is obviously a very good friend.) I suppose you don't have to be drunk - you could be very sick from food poisoning or something else.
So apparently last night, Clark, being the good friend that he is, held her hair while she "worshipped the porcelain god" (threw up in the toilet).
As for the rest, if you "hold someone's hand" you are giving them a lot of guidance and support. She wants to be independent again.
She really sounds like a - well, I shoudn't type that word here. Is she always that nasty to Clark?