Well, that's a very vague description for your character. I'll do my best to answer with the information given, however.
Assuming the girl is now on her own, it's possible to assume that:
A) The girl, with the shock of sudden loss and stress of the situation (you said she doesn't have time), will possible begin to shutdown either emotionally, logically, or even physically. It is possible for a combination of the three to happen as well.
B) The girl might, if she has a very strong personality, force herself to continue on living or doing whatever task she had set out to do and then grieve later.
Speaking of grieving later, that brings us to the next part of your question. Again, I will state that, with the lack of information, the only answers I can give you are terrible. With situation A she might never actually come to accept the loss on her own. In this case, the only way to solve this would be to introduce another character (possibly an old friend of the girl) that can help the girl come to terms with reality. With situation B, however, it would be a lot simpler. The girl will slowly come to accept that her friend (or parent, or sibling, or partner, etc...) is truly gone and you can move the story along to it's normal pace.
Sorry if I'm not much help. I love to answer these types of questions, though. So, if you need any more help, just ask!
—Jack