Start by holding s and right clicking the image. This opens the Google chrome reverse image search. This usually makes or breaks the digging; if there are a lot of results, there's a good chance you're gonna find what you're looking for. If not; it's probably something recently posted or taken straight from Facebook or some other site that restricts reverse searching.

In this case there were a lot of results. The next step is to weed out all the crap sources; things that aren't english, have sketchy domain names, or say things like "HOT NAKED TEENS" as they're probably just single image posts that don't even mention names.

The most promising sources are usually forums, just like Reddit, because often times there have been people in our exact position where someone asked for a source, and someone else replied with sauce.

In this case I had a hit on an archived 4chan post. Someone asked for a source with the OP's picture, and someone replied with a motherless link. In this case it was '/GD467224', which I then entered, and found several images of her as well as her name. Just to be sure this was everything she's posted, I entered her name into Bing and sure enough there was one last image on the net that wasn't in that gallery -- the bathtub selfie.

I compiled all the images onto imgur, rearranged to add a bit of a storyline -- starting with SFW selfies and ending with full spread eagle shots -- and replied with the link.