Learn Hardcore Japanese: kanozyo ha tomodati no memo wo utusite kara, wakaranakatta tango wo zisyoapuri de sirabemasita. - After copying her friend’s notes, she looked up the words she did not understand in a dictionary app.

Breakdown of kanojo wa tomodachi no memo o utsushite kara, wakaranakatta tango o jishoapuri de shirabemashita.

Why is は used after 彼女 instead of が?

は marks 彼女 as the topic: as for her...

In this sentence, the speaker is simply telling you what she did, so は is very natural.

彼女は... = As for her, ...
彼女が... would put more focus on she as the one who did it, often in a contrastive or identifying way.

So here, は sounds like the normal storytelling choice.

What does 友達のメモ mean exactly?

友達のメモ means the friend’s notes or notes from a friend.

The particle の connects the two nouns:

In English, memo usually means a specific written message, but in Japanese メモ often means notes more broadly.

Why is を used after メモ?

Because メモ is the direct object of 写して.

The verb 写す（うつす） means to copy or to transcribe something, and the thing being copied takes を.

So:

Even if English might sometimes say copy from someone’s notes, Japanese focuses on the notes as the thing directly copied.