I think the simple answer is to continue to treat your mother with respect and kindness. The question - What would Jesus do? - really resonates with this question. 
 
We always want to treat others - including those who persecute us - with love and kindness. We obviously need to stand up for ourselves and defend our beliefs, but practically all the time we can do that while dealing with love, kindness, and patience. 
 
Your mother may never accept your choice to be come a member. However, I have seen and heard of many, many examples of people who endured months and years of criticism and ridicule and then finally have the person (i.e. your mother) over time soften and return back the kindness that they show forth. 
 
Even as your mother ridicules you - you can firmly, but lovingly defend your decisions. Just return love for spite. That is always the best advice.

I am from a non member family too. I converted in 2004 while in Basic Training with the US Army. Upon returning home I was met by a very angry and hostile Father when he learned of my conversion.  
 
He too ridiculed the Church and strongly believes that the Prophet Joseph Smith is a liar. He threw out my home teachers and forbid me (an 18 y/o adult) from ever speaking to Mormons again while I lived under his roof.  
 
I quickly became inactive in the Church but always knew that the Church was true though I must admit I had doubts.  
 
I deployed to Iraq, my faith in God was tested in the harsh and cruel realities of combat. I questioned God at times, unable to understand how he allows such suffering. (I still don't understand why, but I accept the God understands why and I place my faith in him!) 
 
I came home met my future wife (next month our first anniversary!) and we started building our life together. At this time I was very confused and not living a righteous life. I drank, smoked cigarettes, and was as far from humble as could be.  
 
But I did still fear God, I just didn't know if he was real or myth.  
 
Long story short, a miraculous recuse from a nasty motorcycle wreck (I was sideswiped on the highway during rush hours and walked away no serious injuries besides road rash) and the spirit sending two missionaries to my door a few months later, got me back on the path! 
 
Since then I have baptized my wife and next month I will be baptizing my mother (on our anniversary!). 
 
I feel your pain in trying to balance your faith with a parent who will not accept what you know to be true. Just know that God has a plan for all things! In all things his will can be done if we have faith (even when we don't know why things are happening the way they are).  
 
My mother was saved by my father's intolerance, my parents are divorced so when my father demanded I get rid of my Book of Mormon I moved out into my Mom's for a month or two before heading out for Iraq. I left the Book of Mormon at her house(by that point I was inactive) and she read it 5 years latter and knew that it was true! 
 
So I can testify that God knows your trials and he knows the reasons for your predicament.  
 
The best council I can offer is to do your best to keep strong in your faith and honor your mother! This is very difficult and you may falter or fall, but rest assured that God knows your heart and has a plan for you!  
 
While the Prophet was wrongly imprisoned by his enemies in Liberty Jail he received the following revelation from God recorded in D&C 121:7-8  
 
"My son, peace be unto thy soul; thine adversity and thine afflictions shall be but a small moment; And then, if thou endure it well, God shall exalt thee on high; thou shalt triumph over all thy foes." 
 
This trial will test you but God will provide a way if you place your faith in him! This trial is for but a moment and the reward for obedience is eternal glory and happiness with God! 
 
 
I hope that your endeavorers are bless and that you hold firm to the Iron Rod and become a great champion for the Lord!