I know of plenty of girls from a wide variety of good seminaries that have email addresses and access to the internet. I feel that realistically the most you can probably hope for even in the frumer seminaries is for them to have filtered internet and even that may be a stretch. I can guarantee that whatever seminary you send your daughter to she will be exposed to girls who have hashkafos that you don’t agree with. I don’t believe that such a degree of sheltering for a girl that age is healthy or practical. The smartest thing to do would be to ask your rav whether such a degree of sheltering is necessary.
