Your mum must be uncomfortable about something. You should find out what this is.
Tell her that the religion as it exists today is not the same one she was baptised into, because there have been so many changes. Even the ministry has changed from teaching people about God, to advertising a website.
(For a list of changes either look here on jw.net, or here on jw.org)
The WT have condemned themselves:
-- WT 5/15/76 p.298 "It is a serious matter to represent God and Christ in one way, then find that our understanding of the major teachings and fundamental doctrines of the Scriptures was in error, and then after that, to go back to the very doctrines that, by years of study, we had thoroughly determined to be in error. Christians cannot be vacillating - 'wishy-washy' - about such fundamental teachings. What confidence can one put in the sincerity or judgment of such persons?"
They claim to be the mouthpiece and channel of God providing food at the proper time. What is proper about serving such bad food that they have to keep removing items off the menu?.
One example is how the decreasing number of memorial partakers was proof that we are close to the end. Now the numbers have climbed higher than at any time since 1960, so what does that do to their 'proof'?
If you don't want to focus on one topic, you can ask your mum to give you one teaching that has never changed, just to emphasize that they are all under constant change. If she says hell fire, immortality of the soul, paradise earth, or the trinity have never changed, tell her that these teachings were established before the F&DS were appointed in 1919, then correct your question to "What teachings from the F&DS (since 1919) have never changed, since only the F&DS are approved by Christ?"
There are none.
As the first WT quote I pasted says, How can you have confidence in that?
Splash