I don't think you can get a solid correlation between length and weight...especially when they are still growing. And as adults, males tend to be (but not always) a bit leaner than females of the same length. When they're growing, they do so at very individual rates. I've got some that seem to put all their growing energy into length before they start packing on the heavier weight....and one that is staying relatively short, but is a little chunk all the time. So long as they are eating regularly, shedding well, and showing no signs of illness...I wouldn't worry about it at all.
Sounds to me like you just startled her. If she just ate yesterday, she may be feeling a bit vulnerable still and did not want to be disturbed.