What are you feeding her? Rats IMO are better for keeping or putting weight on a BP. Also how often are you feeding her/what size? I'm not saying you're doing anything wrong I'm just curious. Have you ever tried power feeding? Power feeding for a short period of time won't hurt. A small rat every 4-5 days should put some weight on her.

As for your question she should be pretty plump, when you hold her in your hand she should be pretty solid. If she's squishy/boney she doesn't have a lot of fat built up. My breeder girl, that I'm hoping will go for me this season, is pretty solid. Granted she weighs over 1.900 grams, but you can really feel all the weight she has on her.

I wouldn't breed under 1,500 grams. A 1,000 gram snake seems too small to breed IMO. Eggs are pretty big and I wouldn't chance losing her.