Hi
Only know the dates for CAT for sure and not professional and that niece has not got any other gifts from the aunt pervious to this to erode the Class B lifetime limit.
Where the valuation date is between 1 January and 31 August, the deadline for CAT payment is 31 October in that year.
Where the valuation date is between 1 September and 31 December, the deadline for CAT payment is 31 October in the following year
Aunt is Classed B band which is 32500 euro threshold Lifetime limit.
But if your Niece was rised by her aunt and have proof of this medical bills payed by Aunt,Education bills payed by aunt and used to live with her aunt. You could have case with revenue to get the band assessed as Class A if the Aunt had a more off a Parent role in her life. ( If you think you have ground for this best to go to tax advisor who could argue the case for you with revenue.For CAT revenue does not define a child so open to the Official you get and how good your tax advisor is. ( Of course this has to based on facts and truefull ) Class A Band is currently €320000.
I work out CAT quickly work out at €253275
I presume a bank would look at issue a mortgage based on normal learning rules and income requirments. But dont know for sure.