I’m surprised that she even wants one. I’ve opened a Tumblr account a few years before, which got forgotten, lent its name to this Steemit account, got briefly revisited but now lies abandoned. Tumblr seems to have a very strange consumer base mainly made up of SJWs and weirdoes and those that are too cheap to set up a Wordpress based blog site. It seems to be madly unregulated, there’s an awful lot of porn on it.
I’d actually suggest helping her setting up a real blog as a father-daughter project and assist her in its creation. She’ll probably learn some real web design skills that way and also be kept away from an international community of wrong ‘uns on Tumblr.
I downloaded the Tumblr app last night and spend a little while browsing this morning. I didn't see anything objectionable, or anything that she would be interested in, frankly.
It sounds like it is popular with teenage girls who like to draw or paint.
It’s only a matter of time before you notice the agendas at play. They pretty much allow anything that isn’t illegal on there.