Sometimes things are explained thru nuance rather than some all-revealing moment...
TBH, especially back then, perception was reality. If someone was perceived a certain way- whether thru mannerisms, style of dress, etc... then that's what they got called. Everybody remembers that one kid in school that you kinda already figured was PROLLY gay. There's even parents who say straight up, they knew their kids were gay before THEY knew they were gay. Juke's moms didn't need to find shyt out or be told. She was tryin' to get her to look more ladylike, that dude tryin to talk to Juke was probably put on to her by moms to see if she liked boys, them dudes Juke knew actin all surprised to see her lookin' like a girl when they were out together... so 1) she doesn't act/look "feminine", 2) she was kinda standoffish to the dude who took her out and tried to kiss her, 3) she hangs out with dudes... nuance.