Can emergency contraceptive pill dleay the second period too?

my girlfriend normally haves her period on 18th (approx 30 day cycle). last month she took an emergency contraceptive pill (ipill), and her period dat months started on 3rd (earlier,, but that is a normal syd effect of contraceptive pills). bt ds month, she ws expecting her periods on 3rd bt dat didnt happn, till now (today's 15th), it didnt start. so she's tensed and confused. is this normal? should she be xpcting her periods on 18th? does emergency contraceptive pills have any effect on the next period, just as it made the nxt one start earlier?