I think that the OP is trying not to put that awkward moment on the shoulders of her daughter, however. And I don't blame her.
I'm surprised that so many are saying the granddaughter should be the one to deliver the news, when it sounds like it was mainly a parental decision. (That the daughter happens to agree with.) I'd never drop that conversation on my kids, especially if I was trying to maintain the grandparent/grandchild dynamic at all.
Me neither. I think it would be really off base to make the child be the "heavy" here. This is a situation where her parents need to have her back. She's 12 and it probably took guts just to tell her parents she didn't want to go--this isn't a situation where she's 18 or 20 and needs to fully fight all her own battles. You get there in steps, not overnight.
To clarify, I don't think the daughter should be the one to break the news to Grandma. I think it's good that the OP's husband made sure to talk to her first.
However, the OP presented two hypothetical conversations of what might happen if the daughter were to talk to Grandma first. The desired outcome seemed to be for Grandma to drop the topic of the trip until she talked to the OP's husband. What I am saying is that I would not expect the OP's "ideal" conversation to get the desired point across to even a reasonable
person, so trying to use it on an unreasonable person seems futile. OTOH, I would expect a statement like "Dad said I can't go, but he wants to discuss it with you himself" to get the point across to a reasonable person, so it seems like a better option to try on Grandma unless the OP already knows that she will react poorly to this. Also, I didn't think the "non-ideal" example demonstrated unreasonable behavior from Grandma--if the daughter asks Grandma to contact her dad, then finding out when is a good time to call seems reasonable. Also, the OP implied that Grandma has never been told that Daughter doesn't enjoy the trips, so she has no reason to assume that Daughter won't want to discuss it.
Based on the OP's examples, I just think it might be worthwhile to re-evaluate how they handle conversations with Grandma. Maybe there is good reason to believe that the OP's examples would be the best way to handle that conversation. But it's also possible that there is a lack of communication that contributes to their frustration with Grandma, because she's reacting to what they say instead of what they avoid saying. If Daughter avoids telling Grandma that she's not coming on the trip, then it's not surprising that Grandma continues the conversation as if Daughter is
coming. If Daughter wants to play along with that assumption until Dad talks to her, that's great, but if she's going to be uncomfortable or frustrated when Grandma assumes she's coming, then does avoiding the issue really improve anything? IMO, it would be more productive to skip that week's Skype call if she's was just going to be uncomfortable either way.