Faithful Witness; You remember what Jesus said to his apostles - "I have many things yet to say to YOU, but YOU are not able to bear them at present.　However, when that one arrives, the spirit of the truth, he will guide YOU into all the truth....." (John 16:12-13)
Just take mom's situation & feelings into account as the priority - not what you'd rightly want for her. Be very gentle with her, because what you have to say to her is very hurtful to most Witnesses. Let her initiate the conversations on Bible/doctrinal topics, and her change of feelings will start to show.
I stopped my research into the old and new covenants 3 years ago because I didn't like what I was begining to see emerge - that I could be believing something that was seriously wrong! I was afraid of the truth. However, I am delighted now that I continued my personal Bible study & research with an increased passion for the truth.
I have a slightly similar situation to yours - my best friend in the cong is a former elder and we have private little chats every so often. I can see & hear by his reaction how distressed he is when I show him a Scripture/literature statement which contradicts the WTBTS. He admits what the truth is, but he can't stop feeding at 'mother's breast'!
He was visibly shaken when I showed him that Revelation 20:1-12 clearly shows that the alleged 'new' scrolls are not opened during Christ's 1000 year reign - they are opened after Satan is destroyed! Such a blatant falsehood is completely missed by most Witnesses, because they accept everything from 'mother' as unquestionable truth!