Mum selling up to live with us

[Kaz]

My mum, who is in her 80s and lives over a hundred miles from us, plans to sell her house and come to live with us. We will be building a "granny annex" by converting our garage and utility room, but we will need to use the proceeds from mum's sale to finance this. I naively thought it was just a matter of her selling up and giving us the money- probably around £80,000. She says that she will be forced to pay tax on the sale.

Any suggestions, please, on how we can best proceed? As you can tell, we are far from wealthy!

Thanks.