Unfortunately I don't have children yet but I have 9 nieces & nephews that range in age from 9 - 24. Because we're the youngest uncle & auntie in the family, they see us as the "cool" ones which means they let me (via FB & Instagram) see a hell of a lot more than what their parents see. It scares the hell out of me. We've had to have conversations with my sisters in law about what their kids were posting (young teenage girls in their underwear on public Insta) and also with the kids about perception by their school peers and also future things like employment.
OP I feel for you as this whole concept scares me for what it will be like when (hopefully) my children reach an age to be involved in this. My two SIL had no idea what the kids were posting, didn't know enough about how to access the media they were using, you sound like you have a good relationship with your DD & it's great that you have access to what she's doing.
We know of someone who applied to be a police officer, in the interview, the police HR pulled out a stack of printed old Facebook posts and Twitter/Instagram likes and pointed out to the applicant highlighted items that they thought were inappropriate for someone applying for that type of job. Needless to say, the application didn't go any further.
This whole area is such a minefield. I think you have to go with your gut, if you feel that they are inappropriate then I think you need to ask her to remove them like you have, but at the same time keep the lines of communication open and explain why. After all you know your daughter, we don't. Do you have someone else trusted that could talk to her supporting what you're saying? We did have some luck talking to our nieces and nephews because we weren't their mum and dad and we're closer to their age so when they were hearing it from someone other than their parents they tended to listen a bit more. Good luck OP!