""The problem is her shifts are made up of groups of different people.""
The real issue is the structure of Care agencies. Low wages and Managers who can't put together shift patterns that work for both the Service User and the Carer.
I've done home care, I've also put packages together for Service Users. The usual is stop smoking half an hour before.
However some people need supervision whilst smoking. I'm a non smoker, but it never bothered me and there will be enough Staff available who it won't bother, so it's about getting the Carer to match the client.
There is a fine line between Care and Control and we shouldn't make people stop smoking completely, to receive Care.
Your relative should take it up with the Agency and not be criticising the Service User to all and sundry.
Is she maintaining correct confidentiality?