My girlfriend (15) is taking the pill. We sleep together a lot. Sometimes she forgets to take her pill. Can she get pregnant?

Yes, your girlfriend can get pregnant.
Taking the pill on time is very important!
But “on time” means different things depending on the kind of pill.

Is your girlfriend taking the mini-pill?
The mini-pill must be taken at the same time every day.
Your girlfriend should set a reminder in her smart phone.
The phone beeps: Now she has to take the mini-pill.
If she takes the mini-pill later or forgets it completely:
Then her protection from pregnancy is weaker.
If that happens, also use a condom during sex until her next period.

Maybe she is taking the regular pill?
Your girlfriend has to take the pill every day.
At about the same time.
If she forgets the pill:
Please also use a condom during sex until her next period.

If she keeps on forgetting the pill:
Go to see a gynecologist, a women’s doctor, together, and get some advice.
There are other kinds of contraceptives.