這句是否有問題？

Lkjgslfjso 你好：
She has written many books for children which she illustrates herself.
她寫過很多由她自己負責插圖的兒童書籍

這句沒有問題，如果分開寫成兩句，不妨可以考慮一下這些改法：
改法 1: 照原文改
She has written many books for children. She illustrates them herself. (沒連接詞)
She has written many books for children. Besides, she illustrates them herself. (有連接詞)

改法 2: 照原文改，但將第二句變成被動式
She has written many books for children. They are illustrated by her. (沒連接詞)
She has written many books for children. Apart from that, they are illustrated by her. (有連接詞)

改法 3: 不照原文，用 author 和 illustrator 來改
She is the author of many books for children. She is the illustrator of these books. (沒連接詞)
She is the author of many books for children. Moreover, she is the illustrator of these books. (有連接詞)

以上是無數改法中的一些改法，希望能夠解答到你的問題！

She has written for children many books which she illustrates herself.
She has written for children many books illustrated by herself.
She has written many children books illustrated by herself.
She has illustrated many children books written by herself.

She has written many books for children which she illustrates herself.

無問題!!!

是無問題的,
She has written many books for children.

She illustrates these books herself.

無問題。
She has written many books for children.
She illustrates these books herself.