Welcome chrisuk, Your email wasn't harsh at all. It was respectful and did not go into any details that the elder could use to alienate your mother from you.
Since you are living with your mother, you have the perfect opportunity to help her by keeping her too busy making new non-JW friends and doing fun activities with you. If your mother has been off and on with the WTBTS, maybe her JW propaganda indocrinators are getting tired of studying with her.
If you want to learn more about how to help your mother think critically for herself, then I would suggest reading Steve 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") and visiting his website www.freedomofmind.com. Don't show your mother what is wrong with the WTBTS, ask her simple questions and help her to learn how to think critically and find answers for herself using the internet, reading books, using the WTBTS Cd, and reading the Bible.
Best of wishes helping your mother to think critically for herself.
Peace be with you and everyone, who you love,
Robert