Family shared books are asking me to purchase again

Me and my mother are in a family account along with other people. I bought a book on apple books with the idea of sharing it with her. When she goes to family purchases, taps my name, she sees the book but instead of a download button it has a price and it's asking me to buy it again. What should I do?

thanks!

My mom has an Ipad pro 9.7, running an ios 15.5 if it matters!