Per this Facebook post she must have died on 22 August 2019:
"British Paphiopedilum Society ·
Fernando Cecilio
· August 22, 2019 ·
Betty Garton passed away in Funchal, Madeira today. She was Sir William Cooke's daughter and lived there since the 1960s.
She managed Quinta da Bela Vista, an old farm that has belonged to her deceased husband's family for a long time where she kept an important orchid collection."
https://www.facebook.com/groups/1843353492551909/posts/2233075253579729/