She is likely not to be pregnant. Periods are often funky after taking Plan B. She can take a pregnancy test now with high confidence it will be accurate, unless you have continued to fool around since that time.
Couple of things. It would be newspaper worth if she got pregnant that way. It doesn't happen.
Second, for future info, you have to take Plan B within 72 hours from the event in order for it to work. 4 days would have been too late.
Third, Plan B is a big dose of hormones. Whopping dose. That's how it works. It creates a situation within a woman's hormonal system so conception can not happen. (why you have to take it within 72 hours of the sexual event). So, once you take it, those hormones are still there. They then have an affect. Late periods, irregular periods, spotting all can go on for 2 to 3 months after you take it.
Which is worth it if you are preventing unwanted pregnancy. But in this case, you weren't. It wasn't necessary to take for fingering. AND, she took it too late to have done anything any way. So, now she just has to deal with the hormonal after affect. good luck