DD and inappropriate instagram

[whathappened]

Hi All, My 17 year old dd seems to really dislike her 14 year old sister.My youngest has just shown me my eldest instagram which has some offensive comments and risky photos.Now my problem is i have promised my youngest i will not let on she has shown me but do not know how to confront otherwise.I do not understand instagram but am told i would need to set up another account to see her posts as they are not private.
Trouble is she will be very suspicious as to why i am looking.
Anyone else had problems with this? Much appreciated.

Just tackle her over it. Are they photos of your youngest? If so she is breaking the law and can be prosecuted for sharing obscene photos of a minor.
Tell her one of your freinds brought yo your attention.

Don't you keep an eye on DDs social media? Not sure what age I'll stop but you could just say you were flicking through and saw them maybe? Or that you wanted to know how it works so asked DD2 to show you and saw them?

Well, in what way inappropriate? With no information, it's hard to give advice.

I have instagram, if it's not private you could pm me her username, I'll take screenshots and send them to you and you can say a concerned adult friend of yours pointed it out?

Thank you so much for taking the time to reply. The photos were of my eldest and her friends in a provocative pose with some of the girls smoking weed.My daughter had put on some comments with a lot of swearing and sexual content! I have just taken her out for our dog walk and started a conversation about someone at work whose child went for an interview but the company had looked at their social media. Think it worked as dd told me there was probably some stuff she needed to delete and she did it with me watching over her shoulder. I am very relieved but as nc4now so rightly says i need to become a bit more savvy with her social media use. Thank you again.

Well played OP, that sounds like it went really rather well!

Don't you keep an eye on DDs social media?
At 17??

My oldest is only 15 but I can imagine having a scroll through his public posts at 17 still. I don't mean monitoring PMs or anything, just casting an eye from time to time.
But I think OP handled it really well.

Clearly at 17 this one still needs an eye kept. That was beyond stupid.