Doubt she's pregnant. If her period was due 4 days later then she would've likely been passed the fertile window. If she's stressing out then that could be why it's late. Also, some women spot for a day or two before their period comes. So again, I'm doubting pregnancy.
but why is she feeling the stomach aches and all, and just having an extremely light amount of blood?
Wait abut a week, take a pregnancy test. But I've experienced the same thing, when condoms break sometimes the body isn't used to the semen especially close to period time so it can throw her period off, plus stress always makes period off. But take a test just in case in about a week because it would be too early to tell now.