Well, the chat is already a bit old, so I din't knoe if the advise has already been given - but there must be any social organisations that help teenage mothers Maybe just show your daughter how the life of a teenage mom becaude of unwanted pregnancy is like and maybe let her have a chat with someone there. And do the same with an organisation of people who got raped. Show her what it is like to suffer from depressions because of that. or to even try to commit suicide. Let her habe a chat wirh someone eho did experience that.
And then let her decide if she agrees to wear a chadtity belt unter conditions she and you and your wife / husband can all agree to.