To deny that Allah is a girl is to state that Allah's transcendent being is limited. Allah's being transcends all categories (including "a girl"), therefore, for any X that exists, it is true that "Allah is X" and "Allah is not X" is blasphemous.
The picture is irreverent, but the objections to it are blasphemy. They deny Allah's transcendence and paint him a a humorless crybaby easily reduced to wrath. The existence of Allah is a matter of faith, His sense of humor is not - one look at a platypus, or in the mirror, proves it by direct observation.
Either laugh and move on, or meditate and repent your arrogant judgment of others. You never know when you might live.