"She may well just be trying to be a good GM"
Well she's utterly failing, if that's her aim.
The children are away, visiting their other Grandma, who they rarely see.
She should wave them off happily and not expect to hear a word until they return.
She doesn't need "contact" whilst they are abroad with family they rarely see, and, far more importantly, neither do the children.
They need to throw themselves into the holiday they are on.
The very idea of you arranging days out, even one day out, around Skyping a possessive grandmother at home is ridiculous.
I am in a similar situation, but it is DH's family overseas. My parents wouldn't dream of intruding on the rare and special time my DDs get with their Grandma while they are away.
Why are you sending her pictures every day? 
The amount of headspace she should be taking up for any of you when you are away is approaching 0.
You'll all be back soon and can see her and show her photos.
There is no need for her to feel included in this. And it's weird and childish that she us trying to force that.
I think you should ask your husband to tell her to back off a bit and leave the children alone to enjoy their holiday.