Should have sent her back a picture of a really big penis. Then she'd be like "OMG Brand, when'd it get so big?!"
I had a coworker show me her boobs once. She had her boyfriend's phone and it had a pic of her boobs on it, so she showed me the pic. :>
Drunk girls like showing off their boobs. Makes them feel special. Definitely should have texted back that it was the wrong person, but in a very congenial manner like Inccubus suggested. Not like, for example, "OMG wait til my friends see this!!!1!"