。
She enclosed a check and sent it to me.
Literal
She [topic-は] check [object-を] enclosing, me [to-に] sent [for me-てくれた].
てくれた marks the sending as a favor done for the speaker — she went out of her way to do this. Without くれた, the sentence would be neutral; with it, the speaker acknowledges the benefit received. 小切手 (literally 'small slip') is the standard word for a bank check, and 同封する is the formal term for enclosing something in an envelope or package. The て-form of 同封して chains it with 送って as sequential actions: first enclose, then send.