The confusion is because the new 738s (first one delivered recently and entered service) have 144 coach seats instead of 132 and the exit rows are 14 and 15 instead of their location on all other AA 738s (13 and 14).

If her seat map shows 14 and 15, she's currently scheduled on a new 738. Problem is, aircraft substitutions happen every day - and I suspect that if you choose 15 and an old 738 is swapped in, you won't still be in an exit row seat. Row 14 appears to be the safer bet, but if booked, what can you do?