。
She's already all giddy with excitement.
Literal
She already ended-up-getting-excited [assertion-よ].
A very casual sentence packed with contractions. The topic particle は after 彼女 is dropped — standard in fast-paced casual speech. 浮かれる means 'to be elated, get carried away.' The ちゃってる is a double contraction: ~てしまう → ~ちゃう (completion/regret), then ~ている → ~てる (ongoing state). もう ('already') with よ ('I'm telling you') gives a 'she's already gone and gotten all excited' feeling.