Stirrup length variations--how to handle during the first lesson

She should start with the average length stirrup. It should be adjusted so that when her leg hangs down the stirrup bottom hits just below her ankle bone. You need to be a super athletic rider to hold a stirrup lower than that, and we know that Hunter's jack them up to more easily enable 2-point. The rest of length is all show stuff and it goes through "fashion" phases.

Here's the simple answer: She should ask the instructor to help her adjust the stirrups so that they are comfortable for her and she can effectively using her legs.