The value of the personal trainer for the average person looking to get into slightly better-than-average shape is dispensing advice along pretty well-understood guidelines
and helping them overcome their self-discipline issues, which is where speaking with the authority of an Olympian adds value even though the training regimes aren't going to be remotely similar.
Of course, she might want to stay well away from her past career for other reasons, whether it's boredom, self-consciousness, frustration or a strong desire to draw a line under it
(FWIW I know an Olympic medallist who made plenty of money from endorsements and speaking engagements and could probably have had a media career but had absolutely no desire to do that or become a trainer/ambassador after his retirement, choosing to became a builder's apprentice instead, because he liked the idea of building stuff rather than because he needed the money)