Thank you for your question
My name is Clare
I shall do my best to help you but I need some further information first
Do they have any chidlren together?
Has S made any financial contribution to the mortgage or to any structural alterations or improvements to the property?
In that case the only right that S has if they separate it to be given "reasonable written notice" to leave - say two months.
However if N dies S will have a claim on his estate 9and vice versa.
I hope that this is of assistance - please ask if you need further details
You are most welcome
So long as they are living together then yes her claim would override a Will and she would almost certainly get a share of the estate