Hi 2pink, Have you asked your mother, "What would cause her to believe that the WTBTS is not God's sole channel to "True Christians" and does not teach Bible truths?" Once you know what will cause your mother to critically think for herself, then help her to independently research the WTBTS and its doctrines - DO NOT do research for her.
One Bible scripture that the WTBTS misquotes and it teaches to JWs as a thought-stopping platitude is in John 6:60-70. Simon Peter's rhetorical answer to Jesus Christ's question is to lead Christians to Jesus Christ and not to a place nor an organization. Also, if Jesus Christ believed in shunning disciples who stopped following him, why didn't he tell the remaining 12 disciples to shun those disciples who left?
Have you read any information by cult-exit counselors like Steven Hassan's books (i.e., "Combatting Cult Mind Control", "Releasing the Bonds: Empowering People to Think for Themselves", and (his latest book) "Freedom of Mind: Helping Loved Ones Leave Controlling People, Cults and Beliefs"), visited his website www.freedomofmind.com, and/or watched his FREE videos on his website?
Best of wishes helping your mother to critically think for herself.
Peace be with you and everyone, who you love,
Robert