。
She can hardly wait for summer break.
Literal
She [topic-は] summer-vacation [object-を] is-impatiently-awaiting.
待ちかねる is a compound verb: 待ち (stem of 待つ, 'wait') + かねる ('be unable to'). The かねる auxiliary is itself a useful stem to know — V-stem + かねる = 'find it hard to V / be unable to bring oneself to V.' So 待ちかねる literally 'cannot wait' = 'wait impatiently for, can hardly wait.' Add ~ている for ongoing impatience and you get the polished 'is eagerly anticipating.' 夏休み, summer break in the school calendar, runs late July through August in Japan — a long stretch off marked by family travel, summer festivals, club activities, and the perennial 夏休みの宿題 (summer homework).