My opinion I think she's probably a bit better off leaner as opposed to heavier for her developing hips.
Given the size that you say she is.....21 1/2"/ 70lbs she sounds as though she is a smaller bitch as minimum breed standard is 22" (at least here in Canada)....but don't worry she's still got time to grow!! She sounds as though she is a nice healthy weight given her age however she sounds as though she is a smaller bitch.
You know it would be tough to say about judges liking fat or big vs proportioned and fit. My young bitch just turned 9 months old and she just finished her Can Ch on her 9 month birthday......even tho she was up against MUCH larger bitches and much older bitches....she could outmove them all even though she's a lean 82lbs and standing 23 1/2". She doesn't have an ounce of extra fat on her but the judges were putting her up anyway so there is hope!!!!
Personally your girl sounds like a good weight given her size!!!
Heather Peters