Question

What inference can be made about Millicent from the way she is characterized indirectly?

Answer 1

Millicent has not always been popular

Answer 2

If this was the missing excerpt:
Millicent sat down at her desk in the big study hall. Tomorrow she would come to school, proudly, laughingly, without lipstick, with her brown hair straight and shoulder length, and then everybody would know, even the boys would know, that she was one of the elect. Teachers would smile helplessly, thinking perhaps: So now they've picked Millicent Arnold. I never would have guessed it.
—"Initiation,"
Sylvia Plath

It can be inferred that Millicent has not always been popular. A lot of people did not take any notice of her. It can even be said that she is a wallflower. Somebody who is there but remains unnoticed.