Thank you for your query at DoctorSpring.com.
Hello again.
Basically her last period was on the 17th of June. Plan B CAN advance or postpone the periods.
As I said, this might be upto a week, sometimes more, upto 10 days. However, it is unlikely that the period has been advanced to this extent, since it is not yet July. I think therefore the spotting / bleeding is withdrawal bleeding, which occurs due to hormonal imbalance brought about by the Plan B pill. This bleeding should subside within 3 - 4 days.
Also, the next period would be unpredictable. It could be earlier or later by the range mentioned earlier.
Take care and I hope this clarifies things further.
I would be happy to elaborate further if required.