I also would like to know this! Just opinions about chicken sweaters in general. Excuse me if I'm mistaken, but aren't chickens sensitive when molting? Would the sweater rub against her and irritate her? Like rubbing a sun burn or something along those lines? Again, not sure, just a thought..
Not only irritate her but a "sweater" or a hen Union Suit, overalls, coveralls, or a parka would bend, and break the new blood feathers because they are as tender as a piece of cooked spaghetti during the molt. A chicken can quickly bleed to death from a broken pen or blood feather. Furthermore the only way to treat a broken pen or blood feather is to pull it out by the roots with a pair of pliers.
I am not going to advise you one way or the other but the things I told you are facts, use them to decide for your self what is in your hen's own self interest.