I spoke to parenting line about it, at the time, and they told me, my most important role, was to look after my relationship with my own daughter, and to not abuse her trust by telling what she confided in me. Especially if it isn't an illegal or abusive situation.
Isn't having sex at 14 illegal then? Just like buying alcohol at 16?

The girls will hopefully thank you when they are mothers themselves, even if their short-term attitude is "oh no, dobbed." And do you really want your daughter to be friends with the type of girl who would do this anyway?