Unfortunately, I don't have a definitive code for you. However, I've got something.
If we look at the male equivolent in the alphabetic index, it sends us to a code narrative reading, "Other testicular hypofunction". So why am I talking about testosterone in the presence of estrogen? Well, if it isn't too far of a stretch, we can use the precedent for coding in testosterone to apply to estrogen.
By my read, you might consider 256.39 (Other ovarian failure)--because those organs are responsible for secreting estrogen--and query the provider for assistance if possible. Give some examples from that 256 category (because I really think that's where your code will come from) and let him/her share the clinical knowledge.
Be sure to let us know what the physician recommends.
Good luck!