Not bad for a first model!
If you're going to keep the texture this low-res though, you should definitely have it unfiltered. I haven't played with SketchFab enough to know if that's on your end or theirs though.
I think her hairline looks too far up on her head. If you look at most heads, even stylized, the hairline comes in just short of 2/3 of the way up. Her hands are a bit blobby right now, I'd recommend making them a little more defined or more circular, depending on what you're going for.
Geometry-wise, there's a few extra loops that don't seem necessary on her back, and especially the back of her hair. If you'd prefer not to take any out, you should beef up the polygons around the rest of her a bit to maintain a consistent level of detail. She's not exactly modeled with deformation in mind either. If you want her to be able to bend at the elbows and such, remember to add at least two edge loops at the joints.
I'm assuming you used symmetry to unwrap her. If you were to unwrap her face without mirroring you could make the eyes slightly different, which would go a long way toward making her look less copy-paste from side to side.