Shelagh Armstrong has a secondary style which she calls her folk style. She uses various approaches to these illustrations that bring to mind great paintings of the early 19th century. This style has been amazing for portraits but is also perfect for editorial and book cover work, as well as packaging design and large format OOH advertising.
Her other style is more contemporary and she uses painterly approaches as well as line and ink. You can see that here: https://www.threeinabox.com/shelagh-armstrong/
You can view more of her work at www.shelagharmstrong.com