CGT payable on sale of property

[CGT a nightmare]

My 92 year old mum has had to move into assisted living as she can no longer cope on her own. We are selling the house so she has money available to live. My question is.... When does she have to pay capital gains tax on the sale of the property, if its not sold, after 9 months, 36 months or never as she has lived there for 46 years so it was her main residence and she is the only freeholder as my dad died in 2009. She is renting the flat in the assisted living complex. She gets attendance allowance, does this make her eligible as she is classed as disabled?. The Assisted living is registered by the CQC but she doesn't at the moment need carers on a regular basis, only for cleaning and keeping a regular eye on her. They do check on her every morning. I have written to HMRC they never reply, I have spoken to them on the phone and one gave the answer never pay CGT as it was her main residence and another we spoke to later (as the first answer didn't sound right) said she didn't know????..... Anyone have any advice, someone must of seen this before?..... If it was a registered care home its straight forward, but assisted living some say yes some say no
Thank you in anticipation

[AGoodman]

Yes, somebody receiving attendance allowance is classed as a disabled person and receives the 36 month allowance.

Even if it you exceeded the relevant period, the relief is proportionate so a few months vs 46 years would be a tiny part of the gain and hopefully covered by the £3k annual exemption.