If she has taken plan-b , the emergency contraception, then the withdrawal bleed after 7 days was expected and its natural . The bleeding has happened within 7 days as it was supposed to be. It has nothing to do with her due dates . THE PRESENT WITHDRAWAL BLEEDING DATE become her fresh LMP and her next menses shall ensue only after a month now after this withdrawal bleed.
The bleed ensures that she is pregnancy safe .
I hope i have answered your query in detail,
wishing you safe sexual practices ,
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