I could write a long response in answering your wonderful post, but I won't. I know how much it hurts. I know how you feel. Despite great odds Mustang was pulled from a serious situation and gotten to you. She left this world loved which is much more than many have when they leave. I, too, have been a caretaker for a few of the kids. Owners that passed on and that is why certain ones came to me. We shall have backyards that adjoin and they will visit (or live with me and visit the other--their choice).
Sending my sympathy. I know how hard you tried and how much you did for her.