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She's at a disadvantage because she's hard of hearing.
Literal
She [topic-は] ear [subject-が] far [is-なので], disadvantageous position is.
耳が遠い is the everyday Japanese phrase for 'hard of hearing,' literally 'ears are far' — the sound is 'far' from the ear. Note a small grammatical oddity: 耳が遠い is built on the i-adjective 遠い, and the standard reasoning conjunction for i-adjectives is just ので (no な): 耳が遠いので. The な here is technically nonstandard — it would be expected after a な-adjective or noun (静かなので, 学生なので), not after an i-adjective. This may reflect a colloquial drift, dialect, or simply imperfect example sentence prose. ~である is the formal copula, giving the sentence a written/essayistic flavor.