The one thing you might want to look into is a transfer now before death. There may be a separate limit between a gift and inheritance. It's been a while since I studied tax, but if there is a death within 2 years of gift the gift is treated as inheritance.
Someone here will probably be able to say if there are two different limits for gifts and inheritance.
If the above is correct (I’m not sure, but it should be easy enough to find out), then your mother could transfer money to you, as a gift, and you could build a home and let her live in it.
Apologies if the two thresholds are connected.