Thanks to https://web.archive.org/web/20150706062443/http://sonypraystation.tumblr.com:80/post/114271949407/how-come-every-time-i-see-a-pic-of-a-fine-thick... from 2015-03-21 or earlier on https://fashionistaswonderland.tumblr.com/archive/2015/3 .. still looking for sauce.
No luck reverse image searching with tineye or google. I believe she's wearing Calvin Klein underwear, not that it helps.
After scanning six months of archives, I was unable to find the proper source. Sorry, internet.