I am so sorry to hear about your baby.

My heart goes out to you.
I can't help answer too well because mine isn't tiny (nor a full Yorkie), but when she was spayed she weighed approx 4 lbs (full grown now she is 9 lbs). I think she was 4-5 months old (I can look it up, but I think thats a close guess).
I am sure many of our other members will reply to you with more info than I can give, I just wanted to give my condolences to you.