this is why you can never say 'impossible' in medicine
if true, she sucked off the guy, swallowed, and was stabbed in the stomach shortly after. the knife probably penetrated some small bowel and her uterus, which were in close approximation to each other. the semen went down her throat, esophagus, through the stomach and a length of bowel (semen contains alkaline fluid to neutralize vaginal acid, but prob works against stomach acid to some degree). when it reached the stab hole it exited the gut, and managed to enter the reproductive system and fertilize an egg.
still sounds like bullshit to me lol