When I came across this article I was quite surprised that I hadn't heard anything about it before. I think that this is a pretty big deal. The #1 American junior who is also the #1 junior in the world and a source of pride for the USTA Player Development is "benched". There are stories about other American juniors on the usopen.org website. Then I remembered that the US Open is a USTA run enterprise and that it can control the flow of information.
I don't see any basis for a lawsuit as others here have stated. I just feel bad for Taylor that her weight has become an issue for them and that the USTA believes that not supporting her for her home junior slam is an appropriate solution. And as a former teenage girl and mother of a current teenage girl, I believe that the quotes that are attributed to Taylor are not thoroughly genuine. She will likely carry some resentment towards the USTA for this.
I believe that fitness is very important for this sport and the USTA obviously knows more about her fitness level than I do. But it is quite possible that she is carrying baby fat and that her natural shape is not to be a svelte and lean Sloane Stephens type. She is not obese and messing around with a teenage girl's head about her weight is just not a good idea.