It is possible - but not very likely. I've heard that even if sperm contacts the outside of the vagina, it can find it's way inside. There are other things to consider such as; her fertility at the time of intercourse. You can calculate that on some websites.. Unless she has an irregular cycle. You should just be patient -- wait for her period, and if it doesn't come, have her take a pregnancy test.

Good luck!!

~krysti