Look at this from your DD's perspective: Talking is hard. Why talk when there's signing?
The primary motivation for kids to work on their linguistics is the need to be understood. She doesn't have that need, and so, she's not working on it. It's not a priority.
One way you might try to make it a priority for her again is to pretend you forgot sign language.
This isn't supported by research. Humans are social animals that want to communicate. Successful communication begets more successful communication. More likely is that either there is something preventing this child from developing the speech abilities, or it's developmental and she'll get there when she gets there.
Islandofapples, the bit I'm picking up on is the lack of consonant sounds. Start with the ped for feedback and screening, and then head on over to an audiologist for a complete workup. My DS' speech therapy for these phonological gaps was pretty quick and painless (at least in retrospect), and it ended up teaching him to read in the process.
We got the brush off from several directions when I was still asking about these things at 34 months. 36 months is the magic age when you get the attention of a ped. If you get the brush off, see if you can consult with a speech and hearing center or university language lab.
