Have you tried moving her up a size of rat, or feeding her a little more often, say every 5 days instead of every 7. For a female, she is a bit on the skinny side, and her head is large for her body size. Picky eaters and slow growers happens, of course, but that doesn't mean you can't try to help her along. I'm definitely not worried by her appearance at all, she doesn't look malnourished at all.