Alison Arngrim really had a broken arm in the Bunny episode
Arngrim was a kid, after all. One day, offset, she broke her arm skateboarding. They worked it into the story of the episode called Bunny. In the story, she falls from a horse named Bunny, mandating she get special treatment. In one scene, she screams; a scream that it turned out was real. The safety rope holding her wheelchair had snapped.