A couple of points
Your mum has had a turbulent life full of ups and downs, the one place she has found stability (and probably a degree of happiness) in her life is in the truth. For her the "Truth" and her way in life is something that represents stability and order as opposed to the chaos that was her life before she found the truth.
Most people that turn to become dubs do so because they are deeply unhappy in their normal day to day lives and what you are effectively doing by asking her to leave is to return to the chaotic world that she once left behind. A lot of people just can't do that.
Leaving the truth means that she would probably piss off her husband and may even loose him. Is she willing to do that? You and I both know he's a d*ck but she obviously feels something for him.
As for trying to turn a dub I think you are going about it the wrong way. Most here will agree that while dubs if we had cold hard anti org facts thrown at us we would shut up our ears and ignore them. We wouldn't listen. Your mum is in dub mode, shes not going to pay attention to anything you have to say about the org because she thinks you are under the influence of Satan.
The only way you can reach people like her is on an emotional level, you cant reason with people like her. She simply has too much to loose, you'll be leaving home in a few years and if you had your way you may well destroy her marriage and then where would she be, single and living on her own again.
My advice would be to leave her to her own life. Let her find out the truth in her own time rather than ramming it down her throat and remember, its a cliche but, you can take a horse to water but you cant make it drink.