Arabesque I think the thing with Nicky, is that she doesn't act sorry. She keeps saying "Who needs the stupid umbrellas anyway?" and she doesn't admit straight away until they say they're going to the police, and the cook (?) directly accuses her.
I remember thinking the instead of a present was mean, but then if you look at the other presents her siblings got instead, then an umbrella was similar price-I think Susan got a book, which also seems mean in today's world.
Nicky's an interesting personality. I don't think anyone would deny she is "difficult", she does deliberately irritate her siblings, jeers at particularly the youngest, but generally wangles her own way. I remember being very irritated when I first read it, when she wangles membership of the tennis club, when she's been told not until she's 10yo, which is younger than when the twins were allowed to join-it also then seems mean on the littlest boy(David?) who presumably will then have to wait until he's 10yo, and then would be at boarding school for term times.
I think the thing with the tennis scholarship, is that tennis has bolstered Susan's image of herself. And Susan is very lacking in confidence. Nicky otoh is brimming with confidence.
Also when Susan has done well, Nicky is, if anything, a bit cross about it. When Nicky does well, Susan is very supportive.
It is a very good character study of a child in a large family who is trying to not be insignificant. In the end, when she truly isn't insignificant due to her talent, she starts to care more about her family, and is a nicer character.
I prefer Party Frock and White Boots of the similar stories.