[Eternal]

To add to what Lizzie said, two days late isn't enough time for it to be a red flag. Periods fluctuate naturally, but it can be due to stress, changes in diet, etc. If you're worried, then have her take a pregnancy test as there is still a chance from just using condoms alone. I recommend getting her on birth control too for better chances at preventing pregnancy. There are options which are long-term and she won't have to remember everyday, such as the IUD.