according to celia, in what way has duke frederick indirectly banished her?

Celia and Rosalind are not only cousins, they are "besties," so to speak. Neither one can get along without the other one. So when Duke Frederick banishes his brother and niece from the kingdom (or dukedom-ha ha), Celia decides to stand up for her banished family members by leaving with them. It is her way of protesting her father's treatment of his kin. So, by banishing the family that his daughter loves so much, he also indirectly banishes Celia. Make sense? :)