Man, my fingers hurt from typing........:chuckle
I usually encourage a pt. to change positions if she's not making any progress in one position. I try pushing that way for about 30 min. if it's the first position we've used and she's a first time mom. If a pt. isn't making progress, I've been known to do everything but dangle them from the light fixtures to try to get the baby out...:chuckle (kidding about the light fixtures, you know).
Anyhoo, I can tell you that when I was a young/inexperienced labor and delivery nurse I didn't change positions with my pts. AT ALL. I know, I know.......you can all give me 40 lashes right now, I deserve it.
I don't know why that nurse wouldn't let your pt. change positions. I honestly can't say without having been there. Maybe she was like I was, inexperienced and just didn't know any better or was afraid to try something new.
I remember vividly the first time I was encouraged to try some different positions. I was that inexperienced nurse, and they had paired me with a traveler nurse for the day to show her around the unit. She had many years' experience, and showed me some great techniques.
As for when they decide to do a c-section, it depends on the doc. That's all I can say. I've seen a c-section called after 1 hour, and I've seen it not called until 4 hours.