Hello oregonseashell!
I also am a military wife with Tricare Prime - it was quite an investigation to find out how to get this covered, but I did it!

I went to the Referral Center on post at the medical clinic and they put me in for a referral under the following:
Nutritional Counseling/Internal Medicine/Disease Management Clinic/(LOCATION).
Then, they gave me the names of two doctors. I then called the TRICARE appointment line and told them the above information and that I needed an appointment with one of those two doctors. They confirmed I'm covered for the Nutritionist appointment and I called and made an appointment.
Hope this helps you!