Zoe was all about trying to fit into Bluebell this week. Therefore, she joined the mayor on his Founder's Day parade float, but there was a problem:
Earlier in the episode, Zoe had diagnosed Lemon's cousin with MS, a secret she wanted to keep from her family. Zoe couldn't tell anyone due to doctor/patient confidentiality, so she made up a story about the cousin having a torn shoulder so she could not participate on her float.
But the Breelands pressured her and the cousin hopped on board the float anyway. When she fainted during the parade, Zoe had to do something -- so she crashed her float! This upset the town, but it at least served a distraction for Zoe to care for the cousin. It was truly a selfless act, really.
But Lemon didn't see it that way, of course. She berated Zoe in front of the entire town.
Still, Mrs. H got the impression that Zoe was ready to take over the practice - oh, she must bring in 30% of the profits or Brick can buy her out - and left the town, mainly because the actress who plays her landed a role on another series.