How to deal with a bully?

there is a girl in my house (i am in a boarding school) who has suddenly become interested in the sport of embarring me in frint of others. i am extremely dim-witted in shooting back answers, and i feel very bad when i just sit and ignore her while she in a mockingly concerned voice says really provoking things. the problem is that she is extremely popular and influential and i do not wish to rub the wrong side of her. what should i do?