If we use the same NPC then we should change the dialogue based on whether you've met her before. Really we should do this anyway, if you repeatedly have pregnant slaves taken away.
I remember the days you set is 150, about a time to notice pregnancy in your eyes. This issue is easy to solve.
If you don't have the permission, day 150 she is taken away normally.
If you have the permission, and you take your pregnant slave to Rosa before day 149, she is no longer a 'slave', 'assistant' or 'prisoner', the interaction will not be triggered.
If you didn't, on day 149, Reverend Blanchett came secretly to ask you for your decision, her belly is too big to have an abortion, if you choose to keep her and have the baby, she must be taken to Rosa today, also Blanchett reminds or warns you, if you break your word, tomorrow she will come with soilders and take her away as ordered without any mercy or friendship. If you choose to turn her in, Reverend Blanchett give you money equivalent to her value.
If you chose to keep her, but you didn't take her away, then on day 150, trigger the event, you get only a little money.
Edit: If you don't have the permission, but you take the pregnant slave to Rosa, she won't be taken away, but have a higher chance to die in giving birth, and baby won't be alive indeed.
I usually have an idea to introduce some new feature system of psychic scars, not so severe like mind-broken, but keeps giving a bad moodlet or even attributes' decreasing in $newloc, such as losing virgin in raping, unwanted pregnancy, a coward seeing you execute a prisoner, and her baby is dead.
But the feature UI space is not enough, and there should be a specific entrance to see her extreme feelings, for example, in the anatomy page, I remember I mentioned before. These information are less useful.
Changing age type, technically like neoplasty, could be done. Theoretically we could implement aging for lolis and young slaves but does anyone play the same game long enough?
Bringing slaves back to life seems unlikely, yes there are liches which means phylacteries and souls surviving outside bodies is possible, but once a soul leaves, bringing it back is a different story. If you are thinking to reanimate a body with the soul of a different slave, it's questionable that you'd be able to restore the same mind and skills of the original slave (or even transfer them from the soul-donor). This is without even considering problems like soul-rejection, soul-incompatibility, and whether a transfer like this is possible. Can a soul, removed from its original body, return to a normal fully-functional body at all, or can it only be bound to a skeleton animated by enchantments (an archetypal lich)?
You are always considering so much in details, I would say, if you aren't ready to design a complex reanimate system not only for your usage, but also works for other game contents, try to make it a simple process, with no probability to fail, but at a high cost to make sure it will never be a worthy deed to increasing her attributes or value.
Most players won't keep a slave for a very long time, so if you want to keep a slave with wonderful attributes, but you want to change her age type or she just happened to die in arena fight, regardless of cost, then you have a chance to choose.
For example, A's soul into B's body:
Beauty to Nature using B's
Pride using A's
All body modifications using B's, affecting Style and Exoticism
Fame cleared
Mood worst, fear 5, despair 3
Habit to Devotion still using A's
All skills using max(0, max(B -1level, A -3level) ), due to a new body.