Tell him. He'll be pissed later if he finds out you knew and kept it.
Well if she is, then theres no point in hiding it so yes you would have to tell him, but other wise, go and get her checked. Its the least you could do, it could help her with alot and also you because maybe thats the reason she came to you for help, not just to tell you her mistake. Give her a lecture and make sure that she understands how shes in the wrong, but she came to confide in you, so DONT TELL HIM (even though I kinda meant it like that back there) its even worse hearing it from someone else.
If she is pregnant she shall tell him, otherwise it is her sex life and shouldnt really concern anyone, just show her and warn her about things, mainly cause in the end it is her decision, and shes going to be the one to suffer with the consequence that she caused. But get her tested and see what all you can do to help, schedual an appointment or something, cause right now shes depending on you.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.