This makes absolute, perfect sense:
Born Mabel Croft in Philadelphia, Pennsylvania, she originally studied painting. Her landscapes were noticed at an exhibition and led to an offer to appear in film.
Okay. A natural progression, I guess. Here's what imdb says:
Mabel Ballin entered the film business in 1917 when Hugo Ballin, her husband, was having little success with his painting career.
He was a painter, but I don't know if that's why she got into the business. Her husband got out of the directing business with the introduction of sound, and became a muralist.
He became one of the foremost muralists in the Los Angeles area, producing murals which still stand at landmark locations such as Griffith Observatory
So if you've seen La La Land, you've probably seen Mabel's husband's work.