"Heifer's moms about 1300 lbs . Heifer weights about800 lbs" - little confusing, I'm going to "assume" you meant to type 80#??? If so, that is not what I would consider small. That's a great size.
The old timers always said you shouldn't keep replacement heifers born out of heifers. BUT, that's because they used super easy calving bulls that produced runts. The new modern bulls being used, can be easy calving with a lot of potential growth after birth.
By all rights, your heifers SHOULD be producing you your best calves, because they should represent your best genetics. Granted, the heifer won't milk as well as a mature cow, so her calves may not wean off as heavy as a mature cow.