I am sorry that Fawn could not adapt, but it is obvious, now, that Fawn knew where she needed to be (with Donna). I am also happy that you are still looking for a friend for Minion.
Now...........a little bundle of orange would make a great "Buddy" (just a suggestion...hee hee)
I have yet another opinion, 6 month old kittens are a real nice age for adoption. Still young and adaptable, but a bit more settled into their personality so you can judge what he'll be like as an adult. And a male would make just as good of a companion for Min as a female. My males LOVE each other and are so much more relaxed.
I guess I could stop rambling now.