Depends how recent the hair loss is, and how severe it is. If it's just minor to moderate, then HRT should take care of it, especially if Finasteride or Dutasteride is added to the mix. And if it's within the last 5-7 years, this should take care of it pretty much completely once 3-5 years on HRT have passed. Pretty much any area where the scalp is not shiny, but still has weakened peach-fuzzy hairs there, it can be recovered. Because the hair follicles aren't dead yet, they've just rendered temporarily inactive by DHT. And once the DHT is removed, they will begin to grow normally again.
If there's large shiny areas, though, and the hair loss was over 7 years ago, HRT probably isn't going to recover it. It will certainly help, but you'll probably need some sort of hair surgery to really get a feminine hairline. (This doesn't mean that you can't pass with just your natural hair, though. I know a lot of middle-aged trans women who have thinning hair, and very clearly not a feminine hairline, but still pass just fine. Once it's long, it covers up a LOT.)
If the top of the head is more or less completely bald,wigs are pretty much the only option. Even hair transplants can only do so much.