Religion is separate from beliefs.
While your mom maybe leaving the religion, that doesn't mean she right away stops believing at least some of the teachings are true.
I have difficulty understanding when some new members first start posting here, say they just left the JW religion so they can now celebrate Xmas and birthdays. That seems to signify they didn't celebrate those things, not because they believed them to be wrong, but only be accepted in the JW religion.
I can however understand a person leaving the religion, doing their own research, and then deciding it is their choice whether to celebrate those things or not.
Your mom started being taught over 12 years ago that those celebrations we're considered by God to be wrong and unacceptable, meaning God will kill her if she does them. Those fears and programing are not going to change overnight but will take some time IF she allows that to happen. Perhaps she will eventually do her own research, and then feel comfortable to reconsider her beliefs including what she now believes about those celebrations.