You can't pregante a jjangshi.
Whether she can get pregnant or not, depends on her type of zombification.
If her body organ functions are really dead, then no she can't get pregnant ever, as the Ova/Egg of a woman only is safe for at max 36 hour post death
(they can die as soon as 2 hours as well), after that there is no way for them to survive.
Even the possibility of her being a surrogate (by using someone else's Ova) is dependent on the type of her zombification.
The only possibility of her ever having her own blood-related child, is if her Ova/Eggs were recovered and stored properly soon after she died.