what made celie become stronger than what she was in the beginning of the book ?

Celie was made stronger by her ability to creatively express herself, her belief in God, and the ability to tell her own story.

Celie started writing letters to God out of frustration and anxiety as she felt alone. It was only a way to give vent to her pent up emotions and stress she was going through. However,in this process of writing letters to God (epistolery novel) ,she finds herself getting more creative in the process of writing as we know how writing is a kind of meditation for some people who love to write. Basically,an escape from the humdrums of life.

Celie found it so relaxing,writing about her experience and views on God,religion and many other things. She finally started writing letters to Nettie whom she found more tangible and 'in reach' and not 'out of reach' as God who would never reply to her.

Through the writing process,she became aware of her present,past and future prospects. It paves way for her independent business and bright future.