by sister i means the nun in the covent
#1 that's not her fault as that stuff is usually carried out by a parent/guardian
#2-4 is contributed by her isolation(etiquette lessons can only get you so far) she needed social interaction by more than a trash fiance, oblivious sister, and useless father
Plus if the family is known for healing and the mc doesn't go outside she would never be exposed to it or even know what to look for if she's a late bloomer
I will agree with everything from #5 onwards usually this type of plot only last about one-shot/1 book so to pad it out they have to withhold information somewhere since the setting is so closed
another dumb fl that 1. doesn't realise not taking the ceremony doesn't mean she doesn't have a skill. 2. doesn't realise that she sees things others don't. 3. doesn't realise she's not powerless. 4. thinks she deserved to be abused and neglected by her father. 5. isn't even the least bit curious about belatedly having the skill ceremony now.
and also why does the sister that obviously pieced things together that the fl has a purifying skill keeps her in the dark? it's like those shitty parents that know their child was diagnosed with adhd or autism but hid it from them and when their child who struggled their whole childhood gets a diagnosis as an adult and tells them, they just go "oh, i knew. you got diagnosed as a child"