Capital Gains Tax & Private Residence Relief for selling overseas home

Hello, I am asking on behalf of my parent's sold home in an overseas country. My parents jointly owned the home, and whist my mother and I lived in the UK since the September of 2021, my father stayed and lived that home up until it was sold in June 2023. While my father is fully entitled to the Private Residence Relief as he met all the criteria set out in the HS283 guidance page - he lived there up until the day it was sold, my mother's situation is more ambiguous due to staying in the UK. Therefore, based on "Married couples and civil partners can only count one property as their main home at any one time" and my father lived there until the home was sold. I would like to ask whether if my mother needs to pay her portion of the Capital Gains Tax, or is she exempt? Kind regards

Hi,
If your mother owns a share of the asset when it is disposed of, then a capital gain may arise. If the property was her main residence up to the date she moved to the UK, then she can claim private residence relief for that period, following the guidance on helpsheet HS283.  
There is a calculator at:
Tax when you sell property
This calculator can be used to work out any gain. All figures used in the calculation must be in pounds sterling, using exchgange rates that were in use at the time of acquistion and disposal.  
The disposal must be declared in a self assessment tax return. Under the terms of Self Assessment, we do not provide an official exchange rate and the onus is on the individual to use a just and reasonable exchange rate for each acquisition and disposal.  
For your convenience, there are exchange rates at:
National Archives: Exchange rates from HMRC in CSV and XML format
For older rates please see:
National Archives: Foreign exchange rates and spot rates: 1 January 1989 to 31 March 2010
You are free to use any of the supplied rates or one of your own choosing.
Thank you.