@Kaarme A lot of bad things have been happened to her throughout the series actually but Kiyo, with her positive personality just brushes them off and moves on. The major bad thing that happened to her is having to give up her dream of being a Geiko due to her being bad and unable to learn the dances. Thing like that would crush people's spirit but Kiyo stays positive. I have seen kids got depression due to them unable to get into their dream university. Kiyo just has so much positive energy and an optimistic outlook on life.
Kiyo is unphased by just about everything. Later on in the story something really bad happens to Kenta, but when the news broke Kiyo was just like "he'll be fine, it's Kenta after all, he'll pull through somehow". That's just her character.
@miyako19 I don't mean that sort of major things. I mean a kitchen appliance suddenly breaking down, a dish failing for some reason, such things, one after another.