Antonia Forest fans

I think there's an element in Rowan's thinking in that she herself is making a hard decision to do something she doesn't entirely want to do, so she is more irritated than usual by Ginty refusing to do something she doesn't want to do. She wouldn't put it like this but something along the lines of 'I'm giving up everything to come and run this farm and she can't even enter a swimming competition!'
It's rather typical of the Marlows to assume that other people in the area would even notice if one of them doesn't enter any competitions, or that anyone outside the family would even care!