Shannon spends every lunch period reading in the back of an empty classroom on the top floor. Nobody can find her there, but it doesn't matter because her classmates don't seem to know she exists. Shannon is a adolescent.

Neglected

Explanation:

Neglected adolescent is the adolescent child that is left apart from care,love and relationship with family, friends and other peer groups. They tends to be alone and connection-less with other people because of facing ignorance.People show low importance to their presence or treat them as non-existent .

According to the question,Shannon is a neglected adolescent as she is ignored by her classmates as if she does not exist and they do not for connection with her either .