if someone is expecting her period the next day and had unprotected sex aday before and took postinor and can not see the period does it mean she is pergnant

It doesn't surely mean that you are pregnant.

When you take an emergency contraceptive your periods will probably be delayed because of the high dose of hormones it contains. It can mess up with your cycle. Your period can be delayed.

Don't be surprised either if you notice some spotting/bleeding after few days of taking the pill.It is also a side effect of the pill. As your period was expected, your next bleeding can be your period too.

However, you've taken the emergency contraceptive and if you have taken it in time, as directed, then its unlikely that you'll get pregnant.

Please keep me updated :)