This is the 1339th most frequent Japanese word.
させる
"させる" means "to make someone do" or "to let someone do."
In this sentence, "させる" is used to indicate causative usage, where the teacher causes or instructs the student to perform the action of doing homework.
先生が生徒に宿題をさせた。
The teacher made the student do homework.
Here, "させる" is used causatively to show that she compelled or caused me to take the action of assisting her.
彼女は私に手伝わせた。
She made me help her.
"させる" in this context reflects the act of compelling or causing the son to engage in piano practice, indicating a continuous or habitual action.