Thanks for your query.
The Plan B
would cause withdrawal bleeding within some days of taking it
What happened on january 22, was the withdrawal period.
Also, Plan b would delay or prepone the normal periods by a week, or sometimes, ten days.
hence you have not mentioned the date of her previous period, it appears that the one of February 15th was her normal one.
If you are too scared , take a pregnancy
test, however pregnancy seems impossible now.