Bait, but I will fucking bite.
Yes, she started out as a total bitch, no one is going to deny that. It's how she develops from a complete bitch to someone fairly kind and loving. The chemistry she develops alongside Fuutarou as she goes from hating him to feeling meh about him to accepting him and then finally loving him was a pleasant treat.
Her banter with Fuutarou is genuinely funny and feels very natural.
I like how headstrong she is about things and how she takes a frontal approach to her situations. She wears her feelings on her sleeve and it creates for some really beautiful moments in the manga. Also her problem of trying to move on from the past to the future resonated with me quite well because of my own personal circumstances I won't get into.
Primarily though it has to do with how she developed from someone who was colder than the arctic to someone with a passionate flame of love.