I'd like to know whether "as was she" is correct in the following:
Peter was aware of the problem, as was she / as she was.
I'd appreciate your help.
Either is correct. In most contexts, as was she is the more common form. The subject-verb inversion is common after as and so. In many contexts, inversion feels very formal or even stilted, but this is still an area where it might commonly be used in everyday speech.
In these phrases, the emphasis is slightly more on the word that comes last. So putting she last is a signal that it is the person that is important in the phrase.
George put his hat on, as Peter did.
George put his hat on, as did Peter.
Both are correct and describe the same set of events. The first sentence places the focus more on the action, the second places the focus less on the action and more on the person.
I am assuming from the sentence that as means "in the way that" or "in the same manner as". As can also be used in this manner to mean "at the same time that", in which case the phrase would not be inverted and typically would not take a comma.