You know your sister, I don't. But, I wouldn't say anyone is disturbed or needs counseling just because they don't like to see obvious displays of breasts in their home. I think it is quite a TYPICAL response of people (Americans anyway) that they don't like seeing women walking around with braless boobs bouncing around. Whether that be on the street, in a business setting, or at home . . . a sizeable majority of Americans want women covered to some extent. An exception would be if the woman is very small-breasted, such that there is no bounce and they can't even tell if she wears a bra or not. So long as a flat-chested woman wears a tee shirt, most probably wouldn't object (any more than they would object if a man wore a tee shirt -- no bounce or boob-shape bumps either way.
As has been noted here, there are other groups and forums that support going topless, bottomless and so on. Likely, the devotees of their sites would think it very wrong if anyone objected to full nudity. And they might claim that those who object are mentally unstable and need counseling. But maybe the truth is closer to saying that such advocates of nudity are the ones out-of-step and hold extreme views.
For any position that you or I take, there is someone who thinks we are totally insane to think that way . . . and any rule we might have governing behavior in our own homes might be judged by such persons as outrageous.