The handsome young mine owner almost DIES, but is nursed back to health by Seth! But then Seth dies, and it turns out that Seth is a woman!!!

Well, that's the "Sweet Polly Oliver" ending I like least.

I would definitely have read a third Frostflower and Thorn novel. There are two other short stories from the same time and I believe a couple of later ones, although I can't vouch for those.