My firstborn stayed at 20lbs forever (or so it seems)! She's just a tiny girl. She potty-trained at 2½ yrs old and the training panties (cloth) were baggy on her!!! None of her shorts or pants fit. I had to use a dog collar to keep them up! (it was a cute, pink leather one!lol). At 8 yrs old, she's one of the smallest in her class and weighs 48lbs! However, she's very healthy and didn't miss a day of school until the last 6 weeks (there's 6 six weeks at her school)!!! And we aren't Asian!!! LOL I'm 5'2" and her dad is 5'8"; so, we aren't very big people.
As long as your daughter is healthy and I see you're giving her vitamin supplements, I'm sure she's just fine :D Especially if her pediatrician hasn't mentioned any concern over her.
Just make sure that the things she does eat (for snacks) is healthy... like apples, oranges, carrots, etc instead of cakes, candy, and chips. :D