Oh hon I'm so sorry. I know you have your heart set on this little girl.
Would you lose a deposit if you backed out? I know it's hard to even contemplate, but you need to be sure that this pup will not put you into financial trouble if you do get her. Especially if you plan on moving out on your own soon.
I really really hope things work out for you. Gosh, I don't know what I'd do if I suddenly found out I couldn't get my little guy. *hugs*