My sister and I work a lot with my mom on her left-neglect due to a stroke. While she does well while we are working with her (specifically her left hand), we are trying to come up with creative techniques, activities, etc. that would help her pay more attention to her left hand on her own.
Maybe get a tennis ball
& ask her squeeze it & watch her do it, with your encouragement.
Don't forget to exercise the affected leg as well or that will get contracted and hard to exercise.
What you need to understand is that the left side neglect is her brain. The damage to her brain has taken away the total awareness of the left side to the world. It shows in "left side neglect"..... but it really her brain that has lost any idea there there is any such concept as a left side to the world.
You can teach her tricks to help compsate...but, you will never be able to teach to compensate for the part of her brain that is dead.
Maybe an occupational therapist might have ideas for you, though?