Oh I so agree wit the guys who feel she forfeited her rights when she became abusive and controlling. She smells like T-R-O-U-B-L-E! If you have to have her come, either because of your wonderfully ethical husband, or because she knows or can find out your address, set firm parameters about the visit. You do not want this puppy showing up unexpectedly or to feel that YOU have now violated the agreement, therefore she can do as she pleases.
I think I would let her know, in writing, that her visit is limited to one half hour, or whatever, and that it is a social visit between her and the horse, that you are not looking for any criticisms or suggestions from her. I would tell her, using quotes from her e-mails, that you found her past remarks offensive, and that any such remarks will terminate the visit.
Finally, if there is any way to arrange the visit to take place at the trainers, even if it means paying for an additional week of training, I would do so, with you being there. You might even say that you are contemplating boarding her there on a permanent basis, so that she HAS to visit there. I know, I know. That darned ethical husband of yours! But still, I would work along those lines, if I could.