More information comes to light...
http://www.thesmokinggun.com/archive/0312042utah1.html
She did eventually have the emergency C-section, but it was too late for the one twin who was already dead (which the doctors already knew at that point, they were just trying to save the other one). She's being charged with child endangerment (not murder,) and not because she didn't want the C-section but because the surviving twin tested positive for cocaine and alcohol. In addition to that, she admitted to smoking pot while pregnant and in fact kept demanding to go outside and smoke a cigarette first before they could begin the C-section.
(edit: oops, sorry--she's simply ALSO being charged with child endangerment of the second one. She's still being charged with murder.)