i think they mention that she uses special preeservation methods that keep her relatively in healthy body parts conditions, meaning no maggots or decomposition, it's just like normal body parts except removable. Plus if one is lost or doe manage to become decomposed she can get replacements.
Actually.
According to the manga, she is a ''modern zombie'', so she has been filled with sterile preservative liquid, so she do not rot. Old times zombies do not have this, so they usually live in freezer rooms.
"filled with sterile preservative liquid"
I read this as meaning she was actually full of liquid. Imagine the sex.
"Oh onii-san I'm gonna-"
RIP
you watch in horror as she slowly deflates, spraying embalming fluid
"This happens from time to time. I've got a patch kit in my purse." Alternatively
Imagine having to use Fix-A-Flat on your zombie waifu.