tjp...it is okay, calm down.
I also flipped out the first time I found a condom in my 15 year old's possession. He is now almost 18. Anyway, come to find out, they had handed them out at school. Though my son thought it was a riot I had worked myself into such a frenzy, lol.
You can not buy single condoms....
You did not find a box, right?
And WORST case scenario...she has protection.
So...after you have calmed down and she comes home, ask her about it.