This depends on the details and on what a prosecutor would want to prove. In German there is an interesting saying that has a lot of wisdom: translated it reads: "You went with them, you will hang with them."
Now, what does the law say: A person can be held accountable for the crimes others committed, when she is an accomplice. An accomplice can be anyone who aids or abets the perpetrators, and that can be by merely encourageing, supporting, assisting the perpetrators. Now, If I as a prosecutor want to throw the book at your friend, I might not have to work too hard to get a jury to agree that someone who obviously is with a group of criminals when they are committing a crime, does not leave the scene immediately etc. must have somehow encouraged, supported or assisted the criminals. (Of course a defense lawyer will work very hard to disprove that).
The question is, if a prosecutor wants to do so. Especially since in your case it seems they have not been arrested? If the detectives go around and try to get those who actually sprayed the property, they might not want to bother with mere bystanders. As long as all her buddies agree she didn't do anything.
So, since this here is all subject to unknown details, I guess she has to wait and see what will happen.
