She's right you know....three weeks isn't enough for you to show her you've changed. YOU know inside that you have changed, that's a given as far as I'm concerned....but you need to try to remember she's lived with you for YEARS trying to get her needs addressed. If she were on this BB instead of you, trying to get advice on how to help the situation...many of us would tell her that three weeks isn't enough time for you to prove you have changed as well. It's just simply not enough time...to prove that your changes are indeed permanent, make sense.
This is going to be tough for you, it's awful to watch someone we love moving further from us....and sure it's not going to be easy to not know where she's going, but eventually I bet she'll tell you. Right now, she needs space to heal. Give that to her.
Until, as you say, she's filed and that ink is dry....there is still hope. In fact there is still hope after that ink is dry that you would reunite.