There is cheap premature baby clothing at K-Mart.
I buy them and then modify the belly side for the Yorkies just so it's not dragging and it just might for your petite kid.
She'll be fine, but understandably you're nervous.
I won't go into my opinions of spay/neuter at a young age, because that's not what this thread is about, but I do want you to know that it's great that you're getting her disiduous teeth removed at the same time, she must not have very many to pull.
My thoughts are w/ you and your little one this week!
