。
She's the spitting image of her father in personality.
Literal
She [topic-は] personality [subject-が] father exactly-alike is.
そっくりだ means 'the spitting image' or 'exactly alike' — a strong statement of resemblance, stronger than 似ている. It's a 擬態語-derived word conveying the degree of likeness is uncanny. お父さん (おとうさん) is the polite word for 'father.' The が after 性格 specifies what exactly is identical: her personality.