It seems to me that shunning is supported by the "sayings of Jesus" in Matthew 18:17:
If he does not listen to them, speak to the congregation. If he does not listen...let him be to you just as a man of the nations and as a tax collector."
I seem to remember the WT saying that the Jews shunned such people. So, it could be said that Jesus was supporting the shunning.
Not that I care, because I have no belief in any god (as Valis stated), but before you debate with your mother, you may want to keep that in mind. When you're debating a JW on the Bible, it doesn't seem very promising because their versions are iron-clad and they usually know quite a bit.
Now, if one were to debate the existence of god, they would be on much more solid ground, imo. As someone on this board said, debating the Bible is parsing a myth.
Pat