I remember Izzy's frustration at not being able to communicate as well as he wanted to. If you haven't already started, try PECS (Picture Exchange Communication System) for some of the words and phrases she needs everyday. We found this system VERY helpful in the kitchen, but not so much anywhere else.
Google "PECS samples" and see if you can find some pictures to print and display.
Also, it sounds like PECS is a replacement communication system, but it was not. When Izzy would use a picture, we would repeat and repeat the word or phrase. Rather than using it as a replacement, we used it to help teach vocabulary.
This still happens to us: Izzy will come up and say something, obviously important. We can't understand him. The look on his face when he realizes we have no idea what he's talking about is really awful! He no longer cries or gets upset (a little upset), but we all know...
Hugs to you and to Becca!! The steps forward are wonderful!!