If you are living in the house with your mother the exemption would apply if

you had resided there for 3 years, the basic requirement for the exemption.

You were living with your mother on grounds of her age or infiirmity. This does not apply for an inheritance.

I would assume, regarding the intestacy that your mother would acquire the house by right of survivorship
John Conlon

dwelling house exemption would apply for CAT

It is amazing how many individuals over look these opportunities ……