Can a 12 year old shih tzu still have puppies.?

Ive had my female Shih tzu since i was 7, she has never been around other dogs and i have never tried to get her pregnant of anything. Recently my mom brought a male Shih tzu to the house (She is supposedly taking care of him, hes been at home for 2 months already) At first he used to always try humping her but my dog would run away or bite him. This past days ive noticed that she is letting him get on top of her. I didn't get her spayed because of her age (and i was scared :{, i never thought another dog would be living in the house) now im worried for her health, is it possible for her to get pregnant. i dint want her to die because of it.