I’m a twelfth-grade girl who, quite evidently, has internet. If this is something that worries you, then probably the seminary I’m interested in isn’t for you anyway, but I can tell you that personally, in my unbiased opinion, I am not tamei. My friends who are applying to BJJ, Bnos Sara, Bnos Chava, Mesores Rochel, Machon Raaya, Meohr, or pick a sem of your choice who all have internet are not tamei either. Any sem you send your daughter to will have girls attending who have used the internet. Now that you’ve asked, at least, you can face the truth and not get a giga shock when your daughter gets back from sem…
The best bet for you is probably to make sure that the seminary she attends does not allow internet access in seminary. It’s at least a start, if that’s what you REALLY want to prioritize. But please, PLEASE focus on the quality of the girls in other areas, the quality of the hanhalah, and so many other factors before crossing off options for reasons like this.