"She found it hard to sing, and claimed it literally 'hurt' to spend an evening in her upper register (which people forget: wasn't required of 'Pirates.' The rock Ronstadt can be heard memorably in act two, thrillingly in 'Go Ye Heroes...')"
Well, that's rather misleading. Those few measures of "Go, ye heroes..." -- I think it's eight measures in all -- were the entire extent of the PIRATES score that Ronstadt sang in her chest/belt register. All of the rest of the role was in her soprano register, much of it quite high-lying.
That said, I'll certainly agree that the role of Mimi in BOHEME is more vocally taxing than Mabel :-)
P.S. I did not see Linda in the role. I saw Patti Cohenour with David Carroll, and the were both excellent.