。
She needs someone to talk to.
Literal
She [topic-は] someone-or-other conversation-partner [subject-が] needed is.
誰か is the indefinite 'someone' (question word + か = indefinite), distinct from 誰も ('everyone / no one' depending on polarity). 話し相手 is a useful compound — 話し ('talking') + 相手 ('partner / counterpart') — for 'someone to talk to / a conversational companion.' 相手 is one of those endlessly productive nouns: 結婚相手 ('marriage partner'), 遊び相手 ('playmate'), 競争相手 ('competitor'). 必要だ ('necessary') marks what's needed with が, not を.