Maybe you could make sure to adopt this precious one to someone with past experience with tinies? Or try to get a sense of the person, and decide if they would stay in touch with you after they adopt her?
For example, 25 years ago, I got my 1st Yorkie, and she was a very tiny girl. I stayed in touch with her breeder throughout her entire life. I have two more Yorkies now, and one of my girls is tiny, and the breeder allowed me to have her because of my experience with my 1st tiny girl.
I can really understand your fear. When you meet perspective parents, go with your instinct. If they don't feel like the 'right' home, don't hesitate to say so. After-all, this is YOUR baby, and you want the very best for her.
Sheila
P.S. You're not a worry wart, you're a responsible person.