At the time of that speech, the Lich was controlling that body.
They are two different minds in one body. When Sweetie P is overcome with fear and terror, the spirit of the Lich inside her comes to life.
The Lich still wins them in two different ways. First of all, the Lich's soul that was in Sweetie P's body that was there was not affected by the elementals. Secondly, he was in the Candy Kingdom during his stay in resin, the Lich stayed there for a long time and was not affected by these powers.
Okay, this is starting to get weird. To be honest, I prefer to remain neutral about the Immo Neg and Regen Neg, because there is some truth to what you are saying.
This is not a delayed regeneration, the Lich was just waiting for the right time.