Zelda may act very perky and energetic, but in actuality, something is very off about Zelda. She once ate a volleyball because she thought it was a giant marshmallow, believes two cloth dummies are her human children, thought that Beef would keep a childhood marriage promise to her (Beef was trying to get back at Kathleen at the time and was super submissive to women) and came to his house uninvited and arranged a marriage, stalks people's public records, believes that aliens exist, and spent all her money on a wedding dress when she wasn't engaged in the first place.
Because of these abnormal beliefs and behavior, it's likely that she suffers from an untreated mental disorder.