Hard to say without proper assessment (like everything, it is just a hypothesis), but honestly I don't think that Abbie will ever learn to speak, let alone form sentences. It is hard to really tell, because the critical period has passed a long time ago, however Abbie was exposed to language from the start. Our brain is wired to acquire language and it needs complete loss of exposure to not learn at all (think feral children like Genie). So i think that Abbie understands quite a bit, but the cognitive software to actually fom words is simply not there.
Fun fact: most feral children and children with inhibited speech acquisition do much better when it comes to sign language. I'd say focus on that. I am not crazy about those made up kindergarden signs though. If ASL is to difficult (and I don't doubt that it is), try Makaton. I don't know why her school kept them for so long. The other thing would be her IPad.
Generally speaking she should focus on single buzzwords. If has a solid vocabulary with a couple of words in every category (and that is a big if), work on two words. And for the love of everything that's holy, Asa, let her figure stuff out on her own without immediately jumping in. Trial and error is so important for leraning.
Sorry for my lengthy posts, by the way. I tend to talk in endless monologues when I like a topic (another Autism trait). I just hope it isn't too annoying.