Thanks, I see that SG and SE maps have rows 7-28 in the economy cabin while AA.com shows 7-30. Further reduction in legroom?
Presumably this confusion is the reason why 13 is taken and 15 is not.
In any event I picked 15C. If it is not exit row on that day, she would be no worse off than in 9C. Plus she gets a chance to find herself in an exit row. For that matter, there's even a chance that her upgrade might come through.