It sounds like your sister is fighting her inner demons and if she pushed her sponsor away, she could most likely be sending the message that she does not have the desire to be clean and sober. At that point, the sponsor cannot help her (because she does not want to help herself) and she does not live within the guidelines of the AA fellowship. Here's some reading on the subject:
http://www.aa.org/pdf/products/m-24_aafactfile.pdf