I don't know anything about LP and pooping, but I do know that anesthetics, pain meds, and the surgery itself can constipate humans as well as animals. That is why they usually make you poo before you leave the hospital after any surgery
I'm glad the surgeon was unconcerned-I hope that little Tatum give you a turd soon
Make sure you give her water to drink and keep her hydrated, that should help move things along.