I don't think there is anything unethical about contacting your therapist after ending therapy especially if you had a good relationship and separation. It's more the other way around that is considered to be ambiguous, for a T to contact ex-clients, but not vice versa. Many people do it, I have done it as well and it's been beneficial (I think mutually).

On modelling your character after her, this is something I would definitely discuss with her first openly and I think it is the right thing to do. Not sure about legal regulations but discussing it first is what feels ethically correct to me, and the opposite might be intrusive, especially if explicit. She might actually be happy to serve as a character model, and perhaps would even learn some things from how you see her in retrospect. I would never do it without consent. I also agree with the other posters about talking to a lawyer if it comes to attempting publication.