kanozyo ha koi no uta wo kaita.

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.

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.

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.

Because 恋 is a noun, not an -i adjective or -na adjective. Nouns usually connect to other nouns with の.

So Japanese says:

恋の歌 = a love song

You can think of it as a noun modifying another noun through の. This pattern is extremely common, like:

日本の映画 = Japanese movie / movie from Japan
学校の先生 = school teacher

を marks the direct object of the verb. It shows what was written.

So in:

恋の歌を
the thing being written is the love song.

The overall pattern is:

topic + object + verb

So:

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

Japanese sentences normally place the main verb at the end. This is one of the biggest word-order differences from English.

English often uses:

subject + verb + object
She wrote a love song

Japanese often uses:

topic/subject + object + verb
彼女は 恋の歌を 書いた

So even though English puts wrote in the middle, Japanese saves 書いた for the end.

書いた is the plain past form of 書く, which means to write.

So:

書く = write / writes / will write, depending on context
書いた = wrote

This tells you the action is completed or viewed as past.

Also, 書いた is casual or plain style. In polite style, you would say 書きました.

Good question. In Japanese, 書く can be used for writing lyrics, poems, articles, and other things made of words. So if the focus is on the words of the song, 歌を書いた is natural.

If you want to emphasize musical composition, Japanese might use verbs like 作る or more specifically 作曲する depending on context.

So 恋の歌を書いた often suggests wrote a love song, especially in the sense of writing the lyrics or creating the song in a general way.

By itself, it does not explicitly mark singular or plural. Japanese nouns usually do not change form for singular vs. plural.

So 歌 can mean song or songs, depending on context. In this sentence, English will usually translate it as a love song because that sounds most natural, but Japanese itself is not marking number the way English does.

Japanese does not have articles like English a, an, and the.

That means a noun like 歌 does not automatically tell you whether it is a song, the song, or songs. You figure that out from context.

So in this sentence, English has to choose something natural, but Japanese leaves that unstated.

Yes, 彼女が 恋の歌を書いた is possible, but the nuance changes.

彼女は feels like:

• speaking about her as the topic
• possibly contrasting her with someone else
• giving background information about her

彼女が feels more like:

• emphasizing that she is the one who wrote it
• answering a question like Who wrote the love song?

So both are grammatical, but they do not feel exactly the same.

Japanese word order is more flexible than English, as long as the particles show each word’s role.

So these can all be understandable in the right context:

彼女は恋の歌を書いた。
恋の歌を彼女は書いた。

Because は and を show what each noun is doing, Japanese can move parts around for emphasis or style. Still, the most neutral and common order is the one in your sentence, with the verb at the end.

Normally, Japanese is written without spaces:

彼女は恋の歌を書いた。

The spaces here are probably added for learners, to make the parts easier to see. This is common in textbooks and beginner materials, but it is not standard in normal Japanese writing.

It is pronounced:

kanojo wa koi no uta o kaita

A few helpful notes:

• は is written ha but pronounced wa when it is the topic particle
• を is usually pronounced o
• 書いた is ka-i-ta, with the i clearly present

So even though the spelling uses は, you say wa here.