I don't recall reading about any instances of KA displaying any unusual vanity, other than you might say her botox treatments, but from what we have been reading on this forum, apparently they are quite common so not necessarily an indicator of unhealthy vanity. KA is a beautiful woman, took good care of herself, apparently (but could have been just blessed with good genes and great metabolism), and accentuated her strong points and natural beauty.
I don't begrudge KA her beauty, and see this case as a love triangle that ended very badly.
But if we are going to look at vanity as part of the case, then let's not leave out CS, whose vanity may have been very threatened by MW, hence his keeping her close. JMO.