Her stylist did a very bad job, her arms do NOT deserve to be on the spotlight. Unfortunately when you take a look at all her red carpets, it’s the only thing you see…
While I'm not a huge fan of the arms, whether or not you have armpit fat and/or axillary breast tissue is largely dependent on genetics and unlikely to go away with weight loss.
I don't think the combination is overly unflattering. Despite, this was not the first time she's been captured wearing something not-so-well fitted...:
IMO, she's always had a more flattering clavicle region, especially because it seems like she has quite narrow shoulders and her breasts are on the smaller side. She will always look smaller in a ballgown-style dress with a sweetheart neckline, compared to (like the image above) an over complicated look that draws emphasis to her legs and hides her thinner features.