K.S.
I'm sorry, I guess I don't see what is wrong with her size.... Are you and your husband tall or bigboned people? Is that why they are worried about her being small??
As long as she's following her curve and hasn't hit a plateau then I personally wouldn't start her on any hormones.
My youngest son is 3 years old and only weighs 26 lbs. He was 7lbs lloz at birth and didn't gain any weight for the first month but did grow in length. He doesn't look unhealthy just a little small but the 3T clothes fit him in length just a little baggy on him so I have never worried about him being little. Our pediatrician was concerned with his slow weight gain as an infant but then she saw my husband who is over 6 ft tall and only weighs 160lbs dripping wet. LOL I guess my point is, maybe it's just her genetics. Maybe she's just going to be petite. Or grow at a different rate. Another thing.... I was in a size 2T when I started kindergarten and I finally grew, not much but I did...I'm 5'2" and although I know that's kind of short but nothing unusual.
I know you are just trying to figure out what's best for your daughter and I'm sure you will. Best of luck to you. :)