Roommate has fishy smell on period?

Sorry for the TMI but I was wondering if anyone knew what this was. When my roommate is on her period and throws her tampons and stuff out in the trash can l, it smells horribly like fish. I have to throw out the trash twice a day to get the smell out of the room. She doesn't seem to notice it and I only notice this smell when she's on her period (maybe just because it wouldn't linger unless she was throwing away something that was near/in the smell). Anyone know what it could be?