Do you know what you think it might be? I am still learning, I'd love to know what issue you have with it
I'm not an artist so I can't give you good artistic advice, however I did study the hard science all my life: biology, anatomy, blah blah blah. I couldn't really figure out what was bothering me at first but i did some little anatomy etches to try to pin point it out.
I think the problem is how the ears and head are connecting. The ears are a bit exaggerated, which is fine and cute and artists should take creative liberties (i looked up how insomniac draws her and found out here ears are actually that god damn big.) Honestly it looks good with the goggles, the strap covers where the ear and head connect. With the headset, to me it looks like the ear is connecting in the way back of the head near the spinal column instead of the more of the side-to-back of the head. I did a crappy little edit to see if it stopped bothering me and I think it did?
I think just removing that line separating the ear and the head makes it look like they're a bit more properly attached, especially with the way her head is facing, we're kind of looking at the side of her head. But with this, it looks like her headphones are full on pointless. They're outputting the sound into her ear flaps rather into her ear canal.
I'm just a dumbass though and I don't like telling artists how to do their art. No need to take my opinions too seriously.