。
She loves birds and flowers.
Literal
She [topic-は] birds and flowers [subject-が] really-loves.
~や marks a non-exhaustive list ('birds and flowers, among other things') — different from と, which would be exhaustive. 大好き ('really like / love') is the emphatic form of 好き. です makes it polite. 鳥や花 is a classic pairing in Japanese aesthetics — the genre of 花鳥画 (flower-and-bird painting) is a traditional art category.