You count from the first day of her last normal period.
For example if her last normal period began on may 20th and if she normally has 28 days between her periods then her next one would have been due on june 17th.
However, taking the morning after pill can mess your cycles up.
Bleeding after taking the morning after pill is normal.
It is far enough past that she should get an accurate result from a pregnancy test by now.
If she gets a positive test then you have 3 options - keep the baby, adoption or termination (for more information or support for this you will have to scroll down to the abortion forums as we don't deal with this subject in here.
If she tests negative and still hasn't had a period within 5/6 weeks of taking a morning after pill then she really should see her doctor to rule out any other possibilities.