I'm so sorry.
Unless you can convince the new owner, who probably loves her to death just like you, to give her back, there's not much you can do. All you can really do is focus on the good (if you're the praying type, pray for strength), and just try to move past it.
I know its impossibly hard. Most of the healing will come with time. It
will take a while, but there will come a day where you'll be okay again. You can get through this. Maybe you can convince the new owner to give her back - I hope you can. But if you can't, then just try to be strong. Its ok to cry though, its necessary to feel better.
I'll keep you in my prayers.