You should be fine. The rule of birth control pills is, if she misses one pill she is fine, just take it whenever she remembers, and take the next pill at the normal time (so your girlfriend forgot saturday, took it sunday at 1:30am and should have taken her sunday pill at the normal time, 8 or 9am). She is still protected from pregnancy.
You can even ejaculate inside her if you want to, and you are still safe from pregnancy. If you are that worried about pregnancy, then you should be using condoms too. Even if you don't ejaculate inside her, there is "precum" that sort of drips out while you are having sex. And it has sperm in it. But she is on the pill so you do not need to worry at all.