Astubchen,
S26 and NAN are equally appropriate for newborns, both are whey dominant and easy to digest. I wouldn't fiddle with the milk now, that'll make her tummy worse because it takes a few days to get used to new formula. Just give it a day or two, most babies have the occasional day where their tummy is sore. A baby is not really considered constipated unless she hasn't had a bowel movement for 5 days. I know you stress as a mom though! As long as she had the black meconium poo in the hospital she is fine for now.
Berry, sjoo, I think I'd also be a bit cross with my mom! Is there absolutely no way you can contact them, or for them to maybe drive to a spot to check in with you regularly? If you go into labour the baby probably won't drop out in 2 hours, so keeping fingers crossed that all will be ok! 4kg is a big baby, but then again, they never weigh as much as the doctors say. My cousin delivered 2 weeks before me by way of induction, perfectly normal delivery (and she is stick-bloody-thin!). She did say that it hurt like hell when the doctor broke the membranes though. Anyways, induction not necessarily C-section, it will all work out for you!