Oh, I'm really sorry to hear things are so bad for your grandma. If she on meds it's important to take it at the recommended dose, as obviously it won't be working properly if she's skipping it here and there (as I know you know, but it's a shame her son and daughter in law are not taking care of this properly!).
We've been having problems with my grandad lately. Totally different situation, he's not eating right and he smokes too much and his health is deteriorating, but I know how it feels to be worried for a loved one and to feel kinda of... helpless? to really help them.
Do you spend much time with your grandma? Does she do anything in her daily life which she enjoys? Those are important things for anxiety too, I think. Is she ok with leaving the house? Just getting outdoors, into nature, helps me a LOT with my anxiety, I just feel so calm when I am somewhere beautiful, plus there are other health benefits.

Good on you for being concerned for your grandma and trying to look after her - I'm sure she appreciates it so much. I hope the doctor can do something for her, when you call him.
x