the question stem quite frankly, sucks.
but, that doesn't mean you can't figure it out.
here's why suppresion is not an appropriate answer:
it is a mature mechanism. the qs sucks, but the behavior of the girl does not seem to indicate a mature response. suppression would be a better answer for instance if the girl herself had cancer and decided to put her negative feelings aside to enjoy a night out (so long as she was aware of her cancer).
blocking isn't appropriate either, as that is a temporary slip-up. think of a student not remembering an answer.
for it to be repression, the idea or feeling has to have been eliminated from consciousness after having being acknowledged. nothing here shows that she acknowledged the pain of her friend dying and THEN forgot it.
that basically leaves denial, here is the key part:
denial does not allow reality to penetrate. it is asserting that some clear feature of external reality is just not true. it is used to avoid becoming aware of a painful aspect of reality.

also denial is not only for the stages of dying!!!