I think we'll have a scene redeeming Elnora. Like, she didn't actually cut up her kid and put her brain in the gundam jar. I bet it was like, some kind of test when they looked into raising permet score even higher (since Eri is not affected, for some reason), and at some point she just became one with the machine, her mind completely transferred there.
Actually, that's would explain where another child that looks like Eri came from. It's just her body. What's the time discrepancy, like 4-5 years? That's around Eri's age.
So, to sum up, a year or so after they run away Eri's mind is gone into the mecha, mindless body left behind, that body learn to live like a person all over again, it was like a newborn, ~16 years later it's Suletta going to school. And her body is older but she thinks she's a teenager, and nobody can tell because she's a small girl that acts like a teenager.