You are right. You should not have let this mother who is under 1 yr old, 3 pounds and in her first cycle to be bred.

This is a VERY bad scenario for both you and your girl to be in and very irresponsible to have taken this risk without researching FIRST. From the situation you have willing entered and the questions you've asked, it seems your knowledge is minimal and now you are playing with the life of your girl.
My advice: Find new vets and new breeders to get advice from.
I hope that for the sake of your little one everything goes smoothly.