Their policy isn’t an unreasonable risk of danger or disruption, it’s an unreasonable risk of offense. You’re not allowed to wear clothes that offend other customers. They can kick you off the plane for wearing a shirt that has an image of giving the middle finger or a curse word. You can tell it’s see through because the collar is fully opaque where the fabric is rolled over itself.

Plus it sounds like they gave the woman the option of changing her shirt or adding a jacket and she wasn’t willing to do that