My sympathies for your loss.
How long did you live in the house with your mam, prior to her passing away? Are your intentions to keep on living in the house, or sell it?
You won't have to pay any inheritance tax if you meet the criteria listed in the link above.
If you sell it, you will have to pay capital gains tax on the sale proceeds that are above the exemption ceiling. The exemption ceiling is in the low 400,000's. By that, you can inheirit a property, sell it, and you are not liable to pay capital gains tax on the first 400,000 of the sale proceeds. You will have to pay it on the remaining 500,000 if the house sells for what you think it is worth. The rate is 20% or 25%. I found myself in the same situation last year. Sorry, I forget the specific numbers re tax rate and the exemption ceiling, so I am ball parking it for you.
There is no getting around the tax. When you sell it, the solicitor will deduct what the capital gains tax is and forward it to the Revenue, before he will hand you over the rest of the sale proceeds.