I'm sad this has happened to your daughter, nevertheless I believe it's your own fault, not Tumblr's (well, someway maybe, the recommendation system could have been made less nasty, people interested in weird content should probably search for it themselves) and not of its users. Every thing should have its corner on the web and you just shouldn't go and let your kids go to those that are not for you. The fact tigers will probably kill whoever they meet doesn't mean there should be no places on Earth where they are not exterminated, just don't go there unprepared. Not every site on the web is to be sterile.

Also really dangerrous and really weird content like that you've described is not going to be affected by the new policy, all it bans are genitals and nipples which actually make nearly as much sense to hide as ears and fingers, people have imagined particular body parts are some kind worse than others and made this a part of the culture but it's not real and just seeing particular body parts can not actually harm a psyche of a healthy human in whatever an age (although I don't insist actual sexual acts can't).