Competent state for sickness benefit

Hi, would love to just run this past someone, working from home and getting brain fog!

My client is a retired Latvian pensioner with a Latvian state retirement pension. He came to the UK as a pensioner to live with his daughter, who is an EEA worker, around 6-7 years ago. They both have Settled Status in the UK

My client gets UK pension credit as someone dependent on an EEA family member who is a worker, although I had to challenge the initial refusal.

His health is deteriorating and his daughter wants to claim AA for him. Would it actually be Latvia, and not the UK, who would be the competent state for a “sickness benefit” for disability, due to the Latvian retirement pension, or is there any argument for UK AA?

Many thanks
Excuse my frazzled head!
Tracey :)