[1] She was the only child of parents coming from Anglesey;[2] her father admired Alfred, Lord Tennyson and educated her on Lewis Carroll and Arthurian legends.
Lilly's first novel, Y Drudwy Dewr (English: The Brave Starling), was published in 1980,[1][3] and is based on her studies of the tale of Branwen in Mabinogion's second strand.
[3][4] Throughout the year of the 700th anniversary of Llywelyn ap Gruffudd's death in 1982, she was commissioned to author the novel Rwy'n Cofio dy Dad to commemorate the occasion.
In 1993, Lilly wrote On A Scaffold High and the short story collection Dynes Mewn Du (English: A Woman In Black).
[2][4] Lilly was an active member of the historical area society of Llanfairfechan and edited and wrote in both English and Welsh on matters of local interest.
[2] D Ben Rees, writing Lilly's obituary in The Guardian, described her as "one of the most gifted children's writers of her generation, and enriched Welsh literature.