Primary Residence Relief PRR - Unmarried Couple Separation

My partner is having some big challenges with separation and finances, and I would like to get some good accurate advice on the subject of selling her home which she shares ownership of with her ex parter. They own it 50/50 as joint tenants. The time has come for her ex partner to buy her out of her share of the property. The total value is £675,000. There is a charge on the property of £70,000. This leaves total equity of £605,000 split evening between them. She lived there with him for 18 years. She left the property in January 2023. The delay between her leaving and getting to this stage has been largely due to his stalling and delaying tactics to avoid parting with any money, but it appears has had a real impact on her CGT liability. Can somebody please advise on what she will be liable for? She does not own another property yet, until she is free from this one she doesn't have enough money to buy another place. Currently she has resided with myself without cost, and has no interest in the property we live in which I own. Their property is slightly complicated in that it was/is a self build, and was originally purchased as a large site with her parents, which was later split for her parents to have the residential property on site, and my partner and her ex to have their new build on a separate deed. She is very intimidated by this sort of thing, and is in danger of being given a raw deal by her ex partner who is very much not intimidated by anything which potentially either saves him money, or causes her upset. If it has a bearing, they have 2 children together, but for PRR and CGT I am not sure that this has any bearing?

Hi  Ben Jordan,
Please refer to guidance here:
Capital Gains Tax: separation and divorce
HS283 Private Residence Relief (2023)
Thank you.