Hi 4get,
There are more than 2 of you in the family, and there must be a sensible way to work out a rota for the calls. Everyone gets a luch break, a tea break etc and since she's staying with your mum, I'm being a little presumptious here maybe.... but why can't your mum call her?
My husbands dad has alzheimers and if we didn't call him everyday to remind him to take the tabs??? then he wouldn't take them, he also has the 7 day packets and also has care workers going in 3 times a day too lol
Can your nan get any help from services?