Personally, I am not a parent, but being teenage daughter myself I feel the need to provide some insight.
Honestly, children will find inappropriate things online. It's unfortunate, and I by no means believe this is a good thing (in my opinion censorship needs to consider young impressionable minds), but the content will be out there. Personally I grrw up with parents who would not restrict me, but communicate with me, when it comes to things that seemed trivial. It depends on your relationship with your daughter, but I believe that educating her on keeping safe is the most important thing.
I've grown up with a lot if adults, usually relatives, who have the attitude of teaching bit also restricting, saying 'never make friends with strangers online. Ect'. The issue with this is that the child may not feel understood and will simply ignore the warning, and online communication has become a lot more common nowadays, so it's best to teach us to be diligent and aware.
For example, I have a friend in America for almost two years now, while I live in Australia. My parents have met her and I've met her parents. Rather than preventing me from talking to her, my parents accept that, while it may feel unsavoury to them, this is what I want to do. They permit me to do it on the basis I am safe and they keep me informed.
So what I would suggest is talking to your daughter about it. It may be awkward - I don't know what kind of 'inappropriate', but I'd recommend being as relatable as possible. I've grown up with three brothers and I can assure you that it is easy, very easy, for us teenagers to do things parents dislike and still fly under the radar.
Good luck :)