Well I just reread your post. I didn't realize you already got rid of her. I think in this case it might be best. It's one thing to feel overwhelmed, it's another to actually dump your new dog because...
If you cannot stop crying, I think you know giving her up is not best for HER. If you believed it was the best thing for your new sweetie you'd be able to let go. I got a dog while in nursing school....