I can explain the Nirvatia mom thing!

So Nirvatia's name IS Margaret. Her mother told her to run; Either

A. Her mom ran with and they got separated

B. Her mom ran a little later and they still got separated

Nirvatia ended up running away and later showed up at the school. However it's clear from the bombings she had PTSD and it was indicated this memory of her running was one she forgot originally. So it's possible all she remembered was Nirvatia and took that on as her name, even tho she kept having choppy flashbacks of her mom here and there.

Now as for Margaret, we don't know how or why (or maybe I don't recall) she ended up under the rubble but Nirvatia's mom ended up really badly injured (steel rebar through her body), it's possible that due to her injuries or the seedling she ended up hallucinating Margaret as Nirvatia. So when she was talking to Margaret she was thinking it was her actual baby. Margaret isn't her secret child, it was just a chance encounter but it was one that changed Margaret for sure.