I'm a 63 yo grandmother. Also a retired police officer who worked often with teens. Here are some ideas. It is natural for her to be curious. Even if she doesn't look it up at home she will have friends who will look it up and she may have access to the computer sights at their homes. You can't stop her from seeing things that you'd rather she not see. However, you can control what she knows about what she sees and as you have been doing all along you can influence the values that she'll embrace. During the teen years the child is developing their own sense of who they are and what they want out of life.
Therefore I recommend first to put the computer in a common room; a room in which someone is apt to see what she's looking up. That will probably be a deterrent to looking up lots of sites.
I would also have a calm and if possible somewhat casual conversation about how you feel about the sites that she saw. Find out why she looked and what she would like to see in the future. Use the sites to teach your values. I don't necessarily mean for you to look them up with her.
But there may be some sites that you could look at together and discuss. Open communication is the key to successfully raising children. And that doesn't mean that you share everything, either. It means you set boundaries while being open to discuss each boundry as it applies to your teen. Some boundaries are non-negotiable while others aren't. Even if you are adamant about sticking to the boundary, discussing it, explaining the reason for it, will help the teen to understand it and be better able to follow it. This also shows them how you make judgements and she will learn by example.
When I was a teenager I complained about the school dress code. My mother wisely said that teens need to rebel and the dress code is a safe way to allow that. I am sorry that schools seem to no longer have rules that would have a harmless effect on the teen when they're violated. We all learn in part by suffering the consequencesof our actions. When the consequences are too high we all lose.