I am lining up a appointment with a  endocrinologist and hear that they often require a recommendation from a therapist.

Mine isn't a gender specialist so wondering what to tell her to wright.

My guess is if she is a gender therapist, your's wouldn't her first clearance letter 

My endo was willing to help me do whatever I wanted to do in order to feel better with or without a letter. HOWEVER, I was and am also seeing a licensed psychiatrist, and my endo knew that. And my psychiatrist did write my endo a letter. A psychiatrist is a therapist who has obtained unto the level of PhD. Basically, she is a licensed physician. In my opinion, you need to find a psychiatrist. An easy way to make sure the person you plan on seeing is a psychiatrist is to ask their receptionist, "can he or she perscribe me medicine?" If the answer is yes, then all should be fine.
I also believe you need a licensed psychiatrist to write you your GID letter.

Psychiatrists are medical doctors (M.D.). They go to medical school  then do one year of internship and then a formal residency in their specialty. A psychologist has a Ph.D in counseling or clinical psychology from a University. Some people has licenses to counsel as a result of training to the Masters level. i.e. clinical social workers. One is not better than the other, indeed non-medical people may have better counseling skills.

As far as what to write.Your therapist can inform the Endocrinologist if you are in need of obtaining hormones on a proper regimine in order to get past any dysphoria you are possibly encountering.It will depend on where your therapist thinks you are in life.Does your therapist see your needs the same as you do?
Best wishes for your future.
Collette