I can well imagine she'd have relied on her script playing Lady Bracknell in her early 90s! LOL. Wilde is devilishly complex linguistically, and doubly so when the script is so familiar to so many audiences. It often seems to me that every line is an epigram. So many of the great Lady Bracknell have been relatively young. Edith Evans was just past 50 when she first played it and Judi Dench was only 48.
Older Bracknells have included Brian Bedford (who was 75 when he did it at Stratford, Ontario). That was his last role, sadly.