If I understand your question correctly – she would not be able to sail below proper course if you came in from leeward.
She must sail proper course and taking you out is not the fasted way to finish.
RRS Definition –
Proper Course A course a boat would choose in order to sail the course and finish as soon as possible in the absence of the other boats referred to in the rule using the term. A boat has no proper course before her starting signal.
My undrestanding and two cents.
Mark