She was willing to give the courtesy of a one-week notice. Courtesy, in that she could have just walked out.
You chose not to accept her courtesy offer for business reasons, and walked her out.
The moment she notified she was leaving, you have the right to accept the resignation and then set business acceptable terms.
It happens all the time in the corporate world.
And for folks that state it hurts her pay, that something that needs to be accounted for when tendering a resignation.