The pill is an extra dose of hormones, so it tricks the body into thinking that there is a foetus developing in the womb like it would in pregnancy. I'm not entirely sure if the pill can delay a period, but it might. Also tell her to stop worrying and relax, as if she is worrying about it a lot then this can delay her period (been there done that). Also if she has only just started to take the pill, then it does wreak havoc with the cycle, so periods can become delayed or they can be closer together. Overall the pill regulates the cycle alot more often, but for the first 3 months the body is getting used to the extra doses of hormones. So that could explain the delayed period.