After following Shady through the woods, Fizzy never (literally never) would have thought that she would see her friend be sucked into a swirling purple light. After thinking it over (not really), she decides to follow Shady and help. After waking up from a short coma, she sees how much braver Shady is, and how Wind Whistler is more emotional (how did she get here, again?). Fizzy doesn't understand, but she'll go with the flow.
Even if the flow is an evil sorceress taking over Ponyville.