Here's a thought gilly, does the care agency provide their workers with moving and handling training? How often do they have to take the course? How long do they have for each visit?
That being said, everything should have been explained to your Grandma, and the reasons given to her for the use if the incontinence product.
In the home where I worked we were not allowed to use transfer boards, and if anyone needed to get up during the night, we had to use a hoist. Lifting anyone on to a toilet or commode was strictly forbidden on health and safety grounds, because if we were injured, or the client fell, the company would be liable.
We had to do endless risk assessments for every task which involved moving and handling.
I hope you soon resolve this matter with the care agency. We are in a similar position with my Dad who is prone to falls these days.