Well, I'm sure you've already had it beaten into your head not to use 2 condoms at once. I know that in theory it sounds good, but like said above, it can actually make it easier for condoms to break/come off. So, now you know that! :) Anyways, from what I've read in the past, pre-cum does not have a very high sperm count. As far as I can see, I think that she was just worried about getting pregnant (being her first time and being 17) and she stressed her body into skipping her period. I think it happens to a lot of girls. Like posters above said, ANYTHING can cause a skipped period. One time, an antibiotic that I had an allergic reaction to caused me to skip a period. So, as you can see, they are tricky things! I really don't think you should be worried. I hope you both have great weeks! :D