My Sim is immortal and I don't know how to remove it

I made a family and for the plot I need one to die. However she didn't die in either house fire she was in, shift clicking and killing doesn't work on her and then when killing her as a last resort through MCCC a pop up saying this Sim is set to immortal came up. 

I don't know how this was applied, nor how to remove it. There are no flags attached to her to remove like being immortal, MCCC is up to date as of a couple of days ago in line with the recent update, and I am at a loss with it.