Her first baptism was and remains the valid batpism. She remains a Catholic, although if she is living with the Bio-Mom, may be taught things about the Catholic Church that are not true. Even if it was the other way around, and she had been baptized in the AG Sect, the baptism would have been valid. But only the first baptism, additional baptisms would not be valid.
What we as Catholics mean by our belief in One Baptism is that when someone is baptized with water, in the Name of the Father and of the Son and of the Holy Spirit. With at the very least the intention of doing what the Church does, the baptism is valid. Even when the person who is doing the baptism holds some erronious theological beliefs, the baptism is valid. In all the the seven Sacraments the Church teaches that the primary minister of the Sacrament is Jesus Himself.
For Baptism, anyone may preform the rite, although the Ordinary minister of the Sacrament is the Bishop or a priest, and the extraordinary minister can be a deacon or any male or female who has reached the age of reason.
The second baptism changes nothing. If the Child is raised from this point on as a Protestant, and decides to come back to the Catholic Church, she will simply have to go to confession. If she had been baptized in a Protestant Church, and never in the Catholic Church, the baptism would be valid, and if she decided to enter the Catholic Church would not be re-baptized in the Catholic Church, but would go through the process of being recieved into the Church where she would renounce the false teachings that she had adhered to in the past, and proclaim that she accepted Theological and Moral teachings of the Church, and would go to confession, then be confirmed.
Any valid Baptism, be it in the Catholic or Protestant church makes one a Catholic, for Jesus did not institute a Catholic baptism, and a Lutheran baptism, and a Baptist baptism. But only one. If one is baptized and joins a Protestant Church at the same time, they were momentarily a Catholic based on a valid baptism, but became a Protestant by the virtue of their entering that other Church, and are described as imperfectly united to the Church.
Many Protestant Sects like the AG, do not accept baptisms administered by the Catholic Church because they do not understand what the Church really teaches. They assume that all Catholics are baptized as infants, (which they do not accept) and they assume that all Catholics are baptized by sprinkling or pouring water on the person baptized, (another thing they deny). We can hope that they thought that they were doing the correct thing, and that they are motivated by untruths they have heard about the Catholic Church. We can pray for them, that one day they may learn the real teachings of the Catholic Church and one day embrace the fullness of the Faith.