Most likely she wasn't a virgin, she was on her period or just starting, which is where the blood came from. This has actually happened to me quite a few times.
If you're worried about blood from a virgin, wait until you have sex with a girl while she's on her period (probably what you saw anyway). Then your priorities change from "let's have great sex" to "let's not ruin the sheets or the comforter" - good times.
If you're worried about blood from a virgin, wait until you have sex with a girl while she's on her period (probably what you saw anyway). Then your priorities change from "let's have great sex" to "let's not ruin the sheets or the comforter" - good times.