。
She gave a beautiful rendition of that love song.
Literal
She [topic-は] that love-song [object-を] very skillfully expressed.
表現する ('to express') applied to a song means rendering or interpreting it — conveying its emotional content through performance. うまく ('well, skillfully') is the adverbial form of 上手い, more idiomatic here than the more formal 上手に. 恋歌 (こいうた) is a classical word for 'love song' that evokes traditional poetic forms like waka and kayō rather than modern J-pop ballads — note how using the kun-reading and the older compound gives the line a slightly literary, formal flavor.