你可以说: "She is very good at swimming." 或者 "She is an excellent swimmer."

这两句话的意思都是她游泳很厉害。

"Good at" 和 "excellent" 都是形容词,用来修饰名词 "swimming",表示她擅长游泳。

例句:

She has been swimming competitively since she was a child, and now she is very good at it.
She spends hours in the pool every day, and it shows in her excellent swimming skills.

中文翻译:

她从小就开始参加游泳比赛,现在她游泳很厉害。
她每天都在游泳池里呆上几个小时,这对她的游泳技术有很大的帮助。