Nice idea...her head looks squashed because of the way you scaled it, and the white tail now looks to be sticking sideways too much. Might look better if you cut away all but the top two tail fethers and replaced with water and a (dark) reflection.
Those feathers on tail look kind uncomfortable to swim. This idea is unique
Kib & Skorpion are spot on. But I also think that the gull should sit a bit deeper into the water...just a bit.