I would say that there are several places on the cast recording where Ronstadt belts. I hate this terminology because I can understand why someone else might use some different terms, but to me she is certainly belting in parts of "Poor Wand’ring One," the interpolated "Sorry Her Lot" and the opening recitative of "No, I Am Brave," not just the parts of "When the Foeman Bares His Steel" that you mention. She certainly sings sections of those differently than a soprano who sang them traditionally would. I’m aware that “Poor Wand’ring One” is lowered a bit, but the reason she sings parts of it with what I would call a belt doesn’t especially matter. Maybe it’s not a rock belt, maybe more of a Broadway belt, what some might call a mix, but to me it’s a belt. (I really hate using this semi-meaningless terminology, but I don’t know how else to put it, and this is the terminology being used here.) I mean, just compare Ronstadt to Elsie Griffin or Elsie Morison (why were two of the great Gilbert and Sullivan sopranos named Elsie?) or Valerie Masterson. If she’s not belting, what is she doing in “Poor Wand’ring One” when she comes in just after the one-minute point, taking over solo after the sisters have sung? I mention that spot because it’s an easy place to cite, but it’s not the only place.
I'm not suggesting, of course, that she belts large sections of her music. I'm just saying that, at least on the cast recording, she belts more of it than just those eight measures you mention (at least what I would call a belt).