。
She doesn't know how to swim.
Literal
She [topic-は] swim-way [object-を] doesn't-know.
泳ぎ方 is a productive shape: verb-stem + 方 ('way / method') makes a noun meaning 'how to do X.' Other examples — 食べ方 ('how to eat'), 使い方 ('how to use'), 書き方 ('how to write'). The form is one of the most useful in everyday Japanese: any verb whose stem you know can be turned into 'how to X' by adding 方. 知らない is the negative of 知る and is the standard way to say 'don't know' — Japanese doesn't use 知っていない (the literal negation of the resultative). Note that not knowing how to swim is mechanically different from being unable to swim (泳げない); this sentence specifically frames it as missing knowledge of the technique.