It was once (is it still?) one of the weirder parts of the internet. For all of the 'gamification' that sites use to encourage community and engagement, tumblrs thing seemed to be collecting mental illnesses and diseases the way other sites might be to level up and advance in rank or unlock emotes and reporting functions. So there were the vampire fairykin tumblrinas and the obese multipersonality ones and slowly and surely it evolved into cesspool of outright madness.

The real mindfuck came when all the xirs log off tumblr, they seemed to take all their celebrated trophy ailments with them. Like they forgot it was just an attention-seeking game and to them it became real. I don't know if its brainwashing or doing mental damage at a time when brains are malleable and formative but regardless, I think you're right in that it played a large part in what was to follow.

Hope things have worked out for the better with your daughter, its a fight that you & the mrs need to keep up with until she develops an immune response to having her head filled up with nonsense. Best of luck.