Is it possible for girlfriend to have late period when having protected sex and not ejaculating in?

Me and my gf have protected sex the times we did it.I popped her cherry last week and then we did it again recently on Monday,she’s says she gets her period all the time on the 27th but now she’s two days late already and the thing is I always had a condom on and never cummed in her.we are wondering and worrying why she hasn’t had her period?