She can wait a period of time and see if she normalizes with her
hormones and begins to get a regular
cycle and if you want, abstain during this period so you have no more 'scares'. Plan B should not be taken again for a while. That is an EMERGENCY contraceptive and you shouldn't have many emergencies in your life time. That has probably created some of the issues with her period.
She also needs to be more responsible with her pills.
one other thing, right now she is unsafe.