Is it possible to impregnate someone through anal sex?

About 6 weeks ago, I had anal sex with a girl I met at a work party. I made it a point not to have vaginal intercourse with her because I didn't have a condom (I know, I opened myself to the risks of transmittable diseases). Anyway, she approached me today saying that some of my sperm migrated from her anus into her vagina. Is that possible? And besides, wouldn't that be her fault? I shouldn't be liable for this child, right?