D..
How's the speech therapy going? What does the therapist say?
Does she look people in the eye? Does she understand direction and what you say to her?
Your speech therapist should have written a report. Go through that report. Look up what the terms she uses mean. Receptive language, expressive language, that kind of thing. Ask her questions after you have researched the meaning of the terms.
There are several things that can cause a child to stop talking. Autism is one. Selective mutism is one, but I would think that she would talk to you, if that were it. And it could be as simple as her learning a new skill and putting talking on the back burner, though that is less likely at her age.
Anyway, talk to the speech therapist. She should have some thoughts two months in to the therapy.
Good luck!
Dawn