Is Delayed Menstruation Post-intercourse Concerning While Having Irregular Periods?

Hi . I had sex with my girlfriend 26th the last month . She had her period starts the month before on 28th . But she has a irregular period circle . Most of the time her period take 10 to 12 more days to come. But after our intercourse after 14 days she haven t her periods. What should we do . its normal or we have to worry about it. Please help.