At 8 months she is heading into adolescence, which is the same as with humans, dogs get ornery and pissy and do stuff they wouldn't normally do! However if she is guardy over food I would make sure everyone is fed and given treats separately, in crates or at least where they can't see each other, to avoid a fight. In the meantime, enforce Nothing In Life Is Free with her (NILIF), she must sit before eating, getting petted, going out. It reinforces your own alpha status.
I don't know about other dog, but most definitely reprimand ANY sign of aggression firmly and consistently. (NO!) usually does it.
Good Luck! Did you post pics?