I agree that homeopathic arnica is perfectly safe during pregnancy. But, I would actually take homeopathic staphysagria if I were you. It is perfect for c-section. It is used to heal cut wounds, and especially reproductive trauma. I would take it *after* your surgery, not before.
Arnica is really more for a bruised feeling, although it is a polycrest remedy ( one the most used) precisely because it is an overall great tonic, so it is likely that it would help you in the instance that you describe. Just not as perfectly as staphysagria would (in my opinion).
Since I see from your signature that you are due in April, do yourself and your baby a big favor and consult a professional homeopath. You will really get yourself ready for birth in a great way.
I also want to add that all homeopathic remedies are based on the principle that they become more potent as they are successed (shaken) and diluted, yes DILUTED. So, any potency that you may choose that is 30C and over, will have no molecules of the original substance used to create it remaining. The little sugar pellets (lactose, generally) are just a delivery device for the energy that remains in the water after the remedy has been diluted and successed. (think Avogadro's number from HS chemistry).
Anyhow, my point is that the energy is what treats you. If you do not resonate with the frequency of the vibration of a particular remedy, that remedy will not have any effect at all (this is what makes h-pathy so safe).
I really recommend a book called Practical Homeopathy by Vinton McCabe. It gives some good background, and it also offers some nice descriptions of major remedies.