Did my girlfriends hymen break?

My girlfriend and I were getting quite intimate. She's 16 and I'm 17, we're both virgins but I've been fingering her for the past 6 months. So today got quite heavy and I pulled out my hands to find them covered in a redish brownish blood. I don't know if its her period blood or if i broke her hymen? Her period hasn't started yet so could it have started while i was fingering her? btw It was a substantial amount of blood about a 20 ml