In order to provide an exact page number, it is necessary to know which edition of the book you are reading. It's also helpful to know if you are looking in the full text or the young reader edition. The quote appears in both texts. In the young reader edition, the quote is slightly different, and it can be found on page 179.

I had once asked God to make me taller. I have realized that God has answered my prayer. God has made me as tall as the sky.

In the standard text version, the quote is found on page 149.

Today I looked at myself in a mirror and thought for a second. Once I had asked God for one or two extra inches in height, but instead he made me as tall as the sky, so high that I could not measure myself.

The quote mentions that the narrator had earlier asked God to make her taller. That is true, and that quote can be found on page 100.

I even promised Allah that if I could grow just a tiny bit taller I would offer a hundred rakat nafl, extra voluntary prayers on top of the five daily ones.

The reason that the narrator wants to be taller is because she wants to be and appear more authoritative. She tells readers that being taken seriously and as a person of authority is difficult when she is so short. She tells readers that she was so short that she could barely see over the lectern and started wearing heels even though she doesn't like them at all.