Basically, I can't get her to talk very much outside of the house - and sometimes even inside the house.
Then you need to look beneath the issue to a reason. Anxiety? Articulation problem? Pragmatic problem? Receptive understanding? Processing speed too slow to answer in time? A psychologist might be able to help to diagnose this but good luck.
I'll second spaghetti's suggestion to look beneath the issue to find the reason. I have a ds with an expressive language challenge - it's not selective mutism, but it appeared to be selective not talking when he was in early elementary school. We thought it was related to shyness or something else at the time, because he seemed to be quite verbal at home, talked a *lot* to us and because of his high abilities when he talked, it was usually language that sounded like an adult. What we didn't realize was that the situations in which he was able to be a chatterbox at home were very different than the situations where he would respond with silence at school. Having a neurospcyh eval at 8 helped to a certain extent by helping us see that there was a very real issue underneath his behavior (he had a few other behavior issues at the time), but what helped the most in realizing he had an expressive language issue was, ironically, another year or so of maturing which enabled him to explain to us that the was having a hard time expressing himself.
Our ds worked with an SLP for several years and it was a huge help, but I think we were beyond lucky and blessed to have landed with an SLP who was really motivated to help him - she said he was unlike any other patient she'd ever worked with, and a lot of her work was a bit of trial and error as she thought of things to try, some worked, some didn't. And as I mentioned, selective mutism wasn't ds' issue, it was an expressive language issue. And for all the work with the SLP and progress he made, he still (in high school) has challenges with expressive language - but he's also been very successful in school. The key for him has been understanding what the challenge is, working to remediate what you can, but at the same time making sure that there are appropriate accommodations so that the language challenge isn't holding a student back from appropriate intellectual challenge.
Best wishes,
polarbear
eta - I mentioned that I felt we were lucky and blessed to find an SLP who was motivated to work with our ds - I hope that doesn't sound off-putting as in you might not be able to find anyone who can help. Once you have an idea of what type of help you need, you can call around, ask questions, network, keep seeking references etc and you'll find the help you need.
