I ran across this YouTube clip of Julia Murney singing Spread a Little Sunshine, coincidentally with Terrence Mann, and she's amazing! I'd love to see her replace Charlotte one day.
She has to be somewhat flexible because she did a very nice leg extension in that video around 2:28.
Charlotte's choreo didn't look that hard to me and I've seen the show twice. Granted, it's not easy, but with a few modifications Julia might be able to pull it off.
I feel that this show highlights each performer's strong points so when they cast replacements, the replacements should do different things. For instance there's a new act 2 opener now that Orion is out. The show is so tailored to the original performers that I don't think they should be very strident in making the replacements pick up where the predecessor left off.
I think what is incredible about Charlotte is she makes the choreography look easy and fluid. its not as simple as it looks. Murney has a gorgeous voice but i dont think she would bring the same dance technique to the role as D'Amboise does.