Gweneth Margaret Howarth Feynman, free-lance landscape artist, world traveler and widow of Nobel Prize-winning physicist Richard Feynman, died of cancer just days before her 56th birthday. Her final illness began while she was on a trip to Egypt. Mrs. Feynman was born in Ripponden, England, Jan. 4, 1934, and came to the United States in 1959. She was one of the key founders of the Noyes Library at Alfred E. Noyes Elementary School in Altadena and of the Arroyo Singers, a non-professional women's choral group that performed in the San Gabriel Valley.