I initially skipped this because over 10K of Eileen Prince is ... well, let's just say a Snape is allowed to have issues with parents. But I'm so glad I finally clicked on this story.
It's brilliant. The three separate POV's work marvellously. Tobias remains rather unlikeable, yet one sees how, from his point of view, he did fair by the lass. And in a way, he was cheated.
Eileen exudes all the bleakness of those who have given up completely, yet she's strong enough to go on with life despite that. Her small triumph when Severus shows his magic is touching, as are the hopes she once had of a live with Sybill.
And Sybill herself! She stays the fey, breathy, scarvy Sybill we know so well, yet there's so much more to her. The teacups, for one must have beautiful things. Her willingness to go to Eileen when Severus is born, and to go again when she feels she needs her. And that final divination, that is actually happy for a change, and that will come to nothing. No wonder she only Sees the gloomy side of things once she's at Hogwarts.