K.S.
Hi there. My name is K. and I don't want to freak you out, so please don't think the worst...BUT my daughter has autism. She never really started talking to begin with, but I have heard cases where the child seemed perfectly fine/normal one day and the next was like a totally different person and no longer did the things they used to. I know you said she does everything else like attempting to walk. My daughter was this way also. No physical restictions whatsoever. Walking and most motor skills were fine. Which is why she was diagnosed so much later than normal autism cases. Usually between 18 months and 2 years is when it's noticed. We did not take her in til she was almost 3.
Sorry I am going on and on here....anyways like I said don't assume the worst and I am not saying that is the problem. BUT if it is a possibility the sooner you find out the better. Beacause the earlier they are diagnosed the sooner they can start taking steps to help them in the long run.
Maybe she is just going through a "quiet phase". I wouldn't worry too much unless it continues.
Hope this can help.
--K.