Celie had plenty of times to leave Mr. if she wanted to.

While the abuse was not full out shown, she was beaten into submission and fear often stopped her when she did try to leave that one time. At least that is what the wiki says, which makes sense in a way. As far as she leaving with her sister. I honestly don't think at the time it would have been possible. He probably would have caught them down the road and brought her back. Like another topic had asked why he kept the letters and one person said he did it for cruel fun. Keeping the sisters apart was probably part of that cruel fun as well. Celie even said it herself at dinner that he took her sister from her because he knew she was the only one who cared about her.

WOW! Poster has obviously never been in an abusive relationship.