It probably wasn't a crutches issue. Perhaps the lady was so incapicated that she would be a hazzard to herself or others in an emergency, or had some other condition which needed a full time nursing attendant.
I have seen it where a family will dump some old geezer on the airline, where the situation should be stopped by the gate agents, but, no, where does the problem end up...?
Without knowing the details of the incident, my ever cynical sympathies lie with the Capt involved.