How was Leak able to leave the church

She has lost all her Scientology friends, but her immediate family also left Scientology, so she is not disconnected from them.

See https://en.wikipedia.org/wiki/Leah_Remini under "Personal life"

Her book explains it best but her family agreed to leave with her which is amazing and rarely happens. But those who are still in it are lost to her. They did disconnect. She still lost friends.