Don;t know your hashkafa, nor your daughter’s age.
I suggest you try telling your daughter in a round a bout way and showing her how special it is your hashkafa, to be shomer negiah, and such things. Try letting her know that being “just friends” is easily lead in to other things if you aren’t careful.
If she knows this and is strong, the friendship will probbobly die it’s own death, being that a boy and girl that are frum have practically no way of doing anything with each other and being avaavilible at the same times.