O_o That's just weird and kinky...
Sperm can't live in the open air for very long. They require a warm, wet environment, with the proper pH balance and moisture content. Even with ejaculation inside a woman, the sperm can die very quickly if these requirements aren't met. So, for them to live on a bed sheet, exposed to the open air for longer than a short while (I've read anywhere from 5-15 minutes) is highly unlikely. Again, this falls into the "it's virtually impossible" category.
Let's assume, though, for the sake of argument, that she did do it and some sperm were still alive. Now the little buggers (who are weak and frail from being in a toxic environment) have to travel from her labia, up through her vaginal canal, through her cervix and down the fallopian tubes. It just couldn't happen. This couldn't get her pregnant.
Again, this is sounding more and more like an hysterical pregnancy. She wants so badly to be pregnant, that she is doing crazy things to try to induce it, and is creating symptoms in her mind.