If you're medically sterile, it doesn't mean you're actually sterile. It takes around 70 days for sperm to become mature. Assuming that she still has the ability to produce sperm,
(1) it would be wise to contact an endocrinologist in the meanwhile
(2) wait for the estrogen levels to wane down as estrogen levels will remain abnormally high even after you stop taking estrogen in comparison to a normal male - this is important b/c estrogen inhibits the proper formation of sperm
(3) see the endocrinologist to get some bloodwork done & ask any questions about fertility
(4) after several months, try taking in a sample of the sperm to be analyzed in the lab to see the motility and such
Some MTF individuals have been able to have children after being on HRT for a long period of time. As everything involving transition, your mileage may vary - YMMV. Good luck. Let us know how the test goes.
Tatiana