In Mozilla Firefox, right click on the image and select "Copy image location" (in IE, it's "Copy Shortcut").  Go to Google and select Images at the top of the frame.  On the right hand side of the search box click on the camera.  Paste the previously copied image location in the search box.  Click on "Search by Image".  I'm sure there's an easier way, but that's how I typically do it.

-- Modified on 1/22/2013 2:32:13 PM

She posted a number of pics with her ad.  Many of them have multiple hits, with the link below showing 6 pages.  With no reviews and pics not being her, my advice is to move on.

When you search, you can't just take the first pic.  Lots of times girls, especially on BP, will include a unique pic (cell phone in mirror shot, etc), but add other pics lifted from various sources.  Check them all, especially if it looks like a studio or posed shot.