You have not quite understood what I said. The house is not shared.
Here is an example of how this works.
Let's say that from 2003 until 2014 the house increased by $100,000. That means only the $100,000 is matrimonial property.
Then lets say the rest of the money in the estate added up to $500,000.
And then let's say your mother had money of her own and it added up to $50,000 and there was a joint account that she got with another $50,000.
So the total matrimonial property is:
$100,000 - increase in value of the house
$500,000 - all other assets in the estate
$100,000 - what your mother has
The total is $700,000.
So she should have $350,000 but she only has $100,000 before she gets money from the estate. So she was entitled to get another $250,000 from the estate.
If she did not get that (this is just an example and you need to use the real numbers but follow my process) then she could have made a claim.
But it is actually too late in any event.
I just felt that you would feel better knowing whether she even had a valid claim.
Is that a bit clearer now?