Hi!
Also as a woman I am not sure about her real intentions. She wants to talk and walk with you but at the same time she wishes you could have somebody to care for you (who could be herself). But then, she is saying that she is married, so maybe she is keeping a distance.
And the use of USTED is really formal here in Cuba. But if she has not seen you for 15 years, that is just a way of approaching you and perhaps next email she will use TU instead.
I believe you should exchange a couple of emails more, asking to clarify her situation with not-so-direct questions but trying to know more about her and her feelings. I don't get that she is not happily married from any sentence.
Good luck!
