Hi and welcome to YT
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What was she eating at the breeder's and what are you feeding now...did something change there...?
Why do you have her at 7 weeks old, as this is wayyyy too young to be separated from her Momma...?
At this age, you truly need to GET HER TO A VET ASAP - no fooling around when you're dealing with such a newborn...it can be a very dangerous time when these babies are taken from their Momma way too soon.