Kiara had been emotionally unstable these days. According to Camden, once his daughter-in-law got pregnant, she started to act more like a Beautiful Lady and would bite someone if she got the chance.
Maybe it's just how pregnant women are, or maybe it's because Aruo Arlong was staying at their home to recuperate, constantly making Kiara anxious and teary, or perhaps it was Kiara's mother nagging her every day at home about what pregnant women should and shouldn't eat or do, babbling on and on, driving Kiara crazy.