No the partner did not adopt this child and the story also leaves out that the birth Mother did abide by the visitation order until her child started comign home and having nightmares and stories of her other Mom bathing with her. When she couldn’t get the court to stop the visitation she fled with her child I assume to protect her from abuse.
I'm not familiar with the laws of the state of VT, but in many states (and possibly VT as well), it is not necessary for a married partner to be granted visitation in custody disputes involving pre-existing children that that spouse did not adopt. It happens all the time.
Second, from what I've read, custody was only granted to the lesbian "partner" after the biological mother refused to abide by the court's visitation order. If what you (and she) alleges is accurate, in this country such claims must be proven by the claimant. I understand that they weren't. I also understand that the biological mother refused to appear at either one, or perhaps several custody hearings. When you are a no-show in a civil proceeding, it shouldn't be a shock when you lose the proceeding. She did the wrong thing here, irrespective how well-intentioned she thought was. She is now a fugitive from justice and there's a reasonable chance she might be facing at least some minimal jail time.