But I do know she is about as personable as an angry viper. For goodness sake, she has a pre-approved gift list, as in "Get me exactly these things". You really don't think she'd be like the fanart shown if someone does something she doesn't agree with?
I have a friend who has given me a pre-approved gift list before his wedding. I was eternally grateful for it. No hassle of having to find something I hoped he and his fiance would like. Just go to the store, buy it, and wrap it up. Simple.
Of course, I come from a family where my mother asked my father for a microwave as a wedding present. He always called her his 'practical princess'. Gift-giving, to us, means asking the perspective 'giftee' what they want, and buying it. So a list like the one Vivienne provides is only sensible in our view.
As to how Vivienne treats the servants, it really is a non-canon source. Making speculations about her character based on it really is far too presumptive. It's possible she's the type to micro-manage, taking the cook into the kitchen and showing her EXACTLY how to make the dish. I doubt it, but it's an equally valid interpretation of her character given the circumstances.
And for all we know, she may have had to make compromises on her dining habits since joining the Inquisition, eating only sparingly, since 'no one at Skyhold knows how to cook'. So if a servant made that kind of effort to get her a dish like the one in the comic, she might be incredibly touched by the gesture, though she may now show it. Again, an equally valid interpretation at this point.