I don't find it particularly implausible - having 2 younger sisters, and having been at boarding school (although never having shared a room at school with my sisters).
We know from other descriptions of life at Kingscote that the mornings are as you'd expect at boarding school - bells, people getting washed, dressed and going to do things before breakfast or chapel. It's not a time for concentrating on other people in your dormitory, so long as they are doing reasonable and expected things. And in the case of the netball switch, they are - one staying in bed, the other getting dressed in the expected manner for netball.
In addition, Ann and Ginty are acting in accordance with their generally-described character - GInty's pretty self-absorbed, Ann's trusting and straight-forward, seeing what she expects to see.
no subject
We know from other descriptions of life at Kingscote that the mornings are as you'd expect at boarding school - bells, people getting washed, dressed and going to do things before breakfast or chapel. It's not a time for concentrating on other people in your dormitory, so long as they are doing reasonable and expected things. And in the case of the netball switch, they are - one staying in bed, the other getting dressed in the expected manner for netball.
In addition, Ann and Ginty are acting in accordance with their generally-described character - GInty's pretty self-absorbed, Ann's trusting and straight-forward, seeing what she expects to see.