Foster Care Support Group
Foster care is a system by which a certified, stand-in parent(s) cares for minor children or young peoples who have been removed from their birth parents or other custodial adults by state authority. Responsibility for the young person is assumed by the relevant governmental authority and a placement with another family found.
My suggestion is to let her prove herself. You can check the history on her computer anytime if you have a concern. Perhaps place a limit on the time she uses it or during certain hours. But from a former foster kid who was never trusted by anyone, give her a chance to prove herself first and go from there.
After all she just might be using the computer for things like homework, or facebook to keep in contact with what friends she may have.
Just an opinion from someone who has been through the foster home thing.
Best wishes!