wow, that is tiny- the breeder should have kept her longer in my opinion. Not even 8 weeks and under a pound
She's just under 13oz, but still...
Be sure to weigh her a lot and make sure she is gaining. Leave food out all the time and watch it to make sure she is eating. Keep a VERY close eye on her because she could easily start to get hypoglycemia being that small and wanting to play with an older brother. Good luck and congratulations on the new baby.