When to start teaching AAC for student with progressive disorder

[pshogg]

I have a student in the 8th grade who is in a Center based classroom for severely involved children.  She has a progressive disorder and is loosing physical, cognitive, and communication functions.  When I first met her in 1st grade she was ambulatory, very social and  independent in communication. (although very dysarthric and slow to get out her thoughts)  She is no longer ambulatory and is now limiting her verbal responses to short sentences.  She appears to no longer have the breath support to speak for any length of time.  The question is:  when do we start teaching her to use AAC so she can continue to communicate?  The SLP (who is inexperienced with physical disabilities and AT) says that as long as she can talk she needs to talk and one shouldn't address AT.  As an OT, I would like to prepare her for the time she is unable to talk, teaching her how to use AT while she is still able to learn, but I really don't know what is considered best practice in this area.  I am completely open to learning.  Can someone help me with this question?