First meetings aka Elsa joins the Just-ice League! Her movie came out last so she gets to be the troubled new kid on the block. The headcanon is spilling crazy fast out of my brain so uh, I’ll try to be brief:
Frozone’s the one who formed the team because he has a soft spot for runaways, particularly if they have ice powers too. He finds Jack first, then Peri, and finally Elsa, who ran away from home because it really sucked to live in a neighborhood where she was known as a weirdo/shut-in. The way they met Elsa was pretty dramatic: she nearly froze Metroville over with her crazy Winter magic. She doesn’t mean to ofc and she actually helps them capture some random supervillain, so in the end she is offered a place on the team and the possibility of special training that could help her contain her powers. All three kids bunk at his place and his wife is actually cool with it…. but she did take her husband aside after meeting Elsa and told him that three was the limit otherwise he should go find himself some nice couch to sleep on for the next three months.