While waiting for a pic....

What were it's previous owners feeding it? What do you plan on feeding it?

You say she is a good eater: was she a good eater for her previous owners? What feeding schedule do you have her on now?

Does her body have a triangle appearance or is she filled out and pudgy?

BTW, her being a dinker doesn't have anything to do with her weight

Hopefully we can help you out when we get the pics. Some are just slower growers than others and some grow in big spurts/steadily.