Well, I know I don't have a girl pyr, but I do have a boy pyr! Girl pyrs are usually on average, I'd say 20 pounds lighter (at adult weight) than a male.
Miles, right now, at 6 months old weighs 75 pounds. He just went through a major growth spurt though. He gained almost 20 pounds in a month and a half. No joke. I'm not sure if he's still considered underweight for his age now, but he was. The vet said he should be a relatively small pyr (about 100 pounds), but that was before his big growth spurt. He is definitely not fat, and doesn't seem thin either (although it's hard to tell through all the fur!)
I would say that Naja is a little underweight at the moment. If she's acting hungry, I'd go ahead and feed her. I would always worry about overfeeding Miles too. But it seems, he only eats alot when he's going through a growth spurt. These past few days, he hasn't been interested in food much at all. But he's acting just fine. It sounds like Naja is going through a growth spurt right about now, and after it's all finished, she could very well be 75 pounds!