Sarie likes pretty things. Even when she was very small, she would wander into Inara's shuttle and run her hands over the silks, try on the jewelry, stare wonderingly at her own face in the mirror. As she grew older and bigger, she played at being a Companion, something that shocked her parents until they realized she had no idea what a Companion actually did.
In her most private thoughts, Inara actually believes that Sarie would make a good Companion. She is lovely, sweet and compassionate, with a sixth sense for loneliness and a complete inability to regard anyone as a monster. She is graceful, or will be when she is old enough, and intelligent, and she has a heart big enough for the entire 'verse. And isn't that what Companions do, after all? Inara has always seen her profession as healers more than whores, despite Mal's frequent declarations to the contrary.
Though of course she doubts anyone on Serenity would let their precious baby go long enough for her to become a Companion. The training is long and arduous; twelve years of study and contemplation before one can even be introduced to society. Too, Sarie at thirteen is a little old to begin the training. And there is always the danger that someone will recognize the name, will see Simon Tam in Sarie's face. No, there will be none of that.
It does make her a little wistful. Sarie has great potential to heal. It isn't just her age, Inara thinks. It's in the way she smiles, her complete innocence, her compassion for the smallest of everything. She is naïve, yes, and if her various aunts and uncles have anything to say about it she will stay that way, unaware of the danger that surrounds her. Their baby.
Everything must pass. Everything must converge and become new, different, older. Nothing is eternal, everything is transient. But as Inara watches Sarie dance around the cabin, wearing one of her old dresses cut down to fit the girl-woman frame, she wishes that Sarie could stay their baby forever.