Barb and Nancy remain friends
Barb and Nancy are good friends. They’ve probably been in big fights before, and they’ve obviously gotten over whatever was said during the argument.
Barb is a supportive friend. I don’t think it’s in her nature to be mean or hold a grudge. Most likely, she’d take Nancy’s barbs, give them back to her, and then they’d probably get over it and move on.
Nancy would show up at Barb’s house later that night and apologize. Barb would hold Nancy’s hand through whatever happened after Jonathan took all those weird photos. Then, they’d see the Demogorgon in the ripped up photos.
Because of their inquisitive nature, they’d reach back to Jonathan, figure out what he was doing and go from there.
Instead of Jonathan and Nancy getting close looking for Barb, they’d become a trio hunting down whatever it was in the woods that night. With Will missing in the Upside Down, Barb would surely do her best to support Jonathan and save his brother or stop this monster.
Barb would, then, become part of the small group of Hawkins residents who know the truth about the Upside Down, Will’s disappearance and the group of scientists doing experiments on kids at the Hawkins National Lab.
Instead of Barb being Nancy’s focus in season 2, we’d see them working together to solve the next problem in Hawkins and at Hawkins High.