kanojo wa koi no uta o kaita.

She wrote a song about romantic love.

Breakdown of kanojo wa koi no uta o kaita.

• は: topic particle
• を: direct object particle
• の: possessive case particle
• 書かく: to write

Questions & Answers about kanojo wa koi no uta o kaita.

Why is は used after 彼女?

は marks 彼女 as the topic of the sentence. It tells you that the sentence is talking about her and then says something about her.

So the structure is roughly:

彼女は = as for her
恋の歌を書いた = wrote a love song

This is different from が, which would put more focus on who did the writing. With は, the sentence feels more like you are already talking about her, or contrasting her with someone else.

Could 彼女 mean something other than she?

Yes. 彼女 can mean she / her, but in other contexts it can also mean girlfriend.

In this sentence, because は marks it as the topic and the rest of the sentence describes an action she did, learners will usually understand it as she. Context decides which meaning is intended.

What does の do in 恋の歌?

の links two nouns together. Here it connects 恋 and 歌.

So:

恋 = love, romantic love
歌 = song
恋の歌 = a song of love, a love song

In English, we often turn this kind of structure into an adjective-like phrase, such as love song. In Japanese, の is a very common way to connect nouns like this.