I believe her height was changed as her look is very, but very commercial, not high fashion.. so when a brand is looking for a commerial girl ( usually the model will work with more models and even male models for a campaing, as an example) and 5'11 is a height for High Fashion modeling, maybe her agency is trying to make her more available to what commerial modeling is, and 5'7-5'9 is a perfect height for it
I know that tall doesnt mean she can model, but I believe she is really pretty, and has an excelent bone structure, its only that she needs more experience in modeling business, like some tips of how to pose, etc... I mean, when a High fashion 16 year old model comes, we dont expect her photos to be flawless, we are more comprenhensive with them, so why can we be the same way with Kendall?? Im sure she will do better in a couple of years