Adult pregnant guinea pig - ceasarian?? HELP!!?

Last week i accquired an adult guinea pig (about 2.5 years old) who is heavily pregnant. I can feel the babies moving around when i hold her. I have read that if they havent breed before there can be terrible complications and she may need a caesarian section. Has anyone had any experience with this?? Also how do I know if she is going into labour?? do they nest build?? Any help would be good. I have a vet appt but not until tommorrow and im worried incase anything happens tonight!