It depends on where the skin tearing is. With my Grandma, it tends to happen on her back. What you can do first clean it and put some antibiotic cream on it. Then to prevent it, what I do is get some baby lotion. I typically use the Little Ones lavender nighttime one. It's cheaper, and in my opinion works so much better than Johnsons. Once a day, just rub it where the major problem areas are that get the skin tears. Then where the "folds are" meaning elbows, knees, wrists, spinal cord, depending on their weight you can put it under their stomach and (for women) under their breasts, put some baby powder on them. That will keep it soft, prevent chafing, and tearing.
I got my mother a pair of "elbow socks" because she was constantly opening up the skin of her elbows. It's a great idea but she didn't wear them. All I can suggest is to keep a good supply of bandages and antibiotic ointment around, and take them whenever you go out with her. My mother has torn her arms and legs in doorways, table edges, getting in and out of car, sometimes not even knowing until we see the blood. I'm not sure there's any way to really prevent it.
My boss has skin that bruises or tears with the slighted tap. This comes with age. So I keep a well stocked First Aid kit.