I have no one to leave me money but I have two siblings. They are in a significantly worse situation financially than me.
We get on well.
If my mother was alive and had an estate to leave, I could understand and support her leaving more to my sisters as I’m fine and they aren’t. My sisters would feel odd about it and require reassurance that I was not upset.
If I’d been left significantly more than them or the same I’d have probably given them more from my share.
Fairness can mean different things.
In OP’s case we have, a large estate, and three siblings who are all homeowners and financially in similar positions.
OP is expected to sacrifice her life and time to care for her mother in her old age.
There is absolutely zero justification for leaving her off except for wanting to.
And if she wants to - why?
There are no valid reasons and that, for me, is why the relationship would be over for me essentially - even if the Will was reversed.
She sees you as a factotum, a functionary, someone to service her. Not someone to cherish.