Age and size are both very important factors in breeding; a female that is too young may have trouble with egg development. A female like yours that is old enough to breed but not up to weight will have little difficulties forming the eggs, but may very well become egg bound, which is when they are unable to lay the eggs.

I'd never breed a female under 1500, preferably 2000. And remember, the bigger she is, the more eggs she will lay.