Anita,
There are different types and manifestations of Langerhans Cell Histiocytosis. Also, the severity of the symptoms can be different. Lastly, I am not sure of what chemo drug they will be giving you. All of that adds up to quite a few unknowns.
I don't think they are going to try it. Chemo can really play havoc on the body and most especially, the liver. Candice, we both know dysphoria. My heart hurts when I tell you this...if they can get a good kill with this round of chemo, it may very well never reoccur. That would be worth the wait.
There is a problem here though. Have you gotten a second opinion of the diagnosis?? Normally, it hits while the person is between 1 and 15. It is most prevalent among Caucasians and females. You really don't seem to match any of that..... Yes, it's possible but second opinion might be reasonable.
Note: I'm not a medical doctor. I am a molecular toxicologist/chemist. My end advice is to get a conformation of the diagnosis and, if they say not to take HRT while on chemo, then don't do the HRT.
Hugs,
Jen