Her proportions are rather odd:

1: Her head is too large for her body. Male Engie, even as the shortest man of the group, is 7 head-lengths tall. This makes her look younger than you may have intended for her to be.
2. The crotch should be the halfway point of the body. The way you have it now, either her legs or her upper body is too short.
3. Her knees, as suggested by the placement of the knee pads, are too low.

You may also want to consider a different angle for the pose because her face has no real shape or volume to it. One of the reasons TF2's style is so awesome is that our dudes are Real Manry Men with Craggy Manry Menfeatures. You did well in suggesting her musculature, but give some character to her face. (Look up "women's face shapes" or somesuch to help.)