from what i understood, i think it was if sunlight touched her she turned into a human but because they were underground and always did things at night she stayed an ogre. Or something along those lines
I liked how it showed how a "happy" idylic family life can be dull, annoying etc but we have to stick with it, also we don't know what we've got til its gone
Overall it was more emotional than I thought it would be and the story was a clever way to end the series.