I guess the reason I asked this question here is I was wondering if what Reba did was really all that bad (I don't think it was), or if the hostess' feelings about her colored her opinion. She clearly doesn't think much of Reba, and I wondered whether, if someone else had asked the same thing, the hostess would have thought it was that much of an outrageous request.
Honestly, if I were the hostess, as I said before I wouldn't have given it a second thought. If I were Reba? It would depend on who the hostess was. I probably wouldn't ask, but if it was someone I was very close to (certain close friends, or family members) I might ask but offer to cut and serve the dessert for my SO or whoever wanted it myself, so as not to cause the hostess any trouble. If she then offered to do it, great, of not, so be it.
It wasn't anything that required any special preparation or presentation. And the hostess was not "just sitting down for the first time in several days" after preparing for the party - she had been sitting and socializing for quite a while before dinner was served, and dinner had not been homemade - it was a few things that had been heated in the oven, and a couple of deli platters, all of which had been ordered from outside. Of course, there was still preparation necessary, but she didn't spend days beforehand cooking, nor did she spend the whole pre-dinner time at the party cooking. Not that it matters, really, I just wanted to clarify that.