Yep, depression. It sometimes happens after giving birth, but I suspect it might've started that way but now it's taking over her life. And sending her away somewhere by herself, leaving her alone, won't going to help.
Looking at the society described here, I'm not sure they know what to do with depression (although someone realized that she needs to "rest her mind" which sounds like a good start, but it's only that: a start). Seems like it's been festering and will be festering for a few more years as we've seen.
I just... when do we get back to the "present" time? And what will be Harsen's reaction then? Will he see her sincerity and heart? Or will he turn away from her (troubles) again?
And let's not forget how difficult it must've been for little Vincente in all this. Neither of his parents seem to particularly care about him. Harsen might admonish Ercella for not having a meal with Vincente or not spending time with him, but I don't see him doing it any differently. Of course, in that society, taking care of children was the job of the woman and men could care less about the matter. Really, really sad.