yeah - I read all of this as Tama being the "normal" one—i.e. the one who didn't suffer severe trauma, and thus will be instrumental in helping the others heal, as they all help one another heal as well.
She also doesn't "need" a big tragic backstory; she's the lens character of the series (for the most part), and so having someone who isn't carrying a metric tonne of narrative baggage who can be the primary perspective for the reader means that the others can have their stories focused on more effectively. Her being more even-keeled provides a bit of a contextual contrast that the other characters can be compared against, and she gives readers someone to relate to in a series that has a lot of heavy stuff happening.