Pretty sure it is. This is something she does. (Probably not entirely sober at the time.)
Mod edit: I agree there's a strong resemblance, but the fact that I can't recall seeing her do much (any?) public nudity, let alone with civilians nearby/in the frame that makes me wonder whether it's really her... it just seems a bit out of character for her (though certainly NOT out of the realm of possibility). The laughing/squinting thing and general poor quality of the photo make it hard to compare to Tessa pix to be sure. Shall we continue to consider this undecided for a bit and see what others think? Maybe someone will turn up similar selfies known to be her and we can use them to help authenticate this one? -Pal