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A New York appeals court has found in favor of a Chinese teen who was adopted by a wealthy couple and then given up for adoption again, ruling that she is entitled to a portion of her first family's $250 million estate.

In 1996, John and Christine Svenningsen of Westchester, N.Y, adopted a baby girl from China, whom they named Emily Fuqui Svenningsen. Before finalizing the adoption, the couple, who already had four biological children, had one more biological child. Around that same time, John Svenningsen, a party goods magnate, was diagnosed with cancer, according to court documents.

On May 6, 1996, the Svenningsens signed an adoption agreement stating that they would not abandon Emily or "transfer or have [her] re-adopted," and that she would be deemed "a biological child," according to court papers in the case. The agreement also stated that Emily had the right to inherit the estate of her adopted parents, who had established a pair of trusts for their children, as well as one meant solely for Emily.

John Svenningsen died in May, 1997.

In December 2003, Christine brought Emily to The Devereux Glenholme School in Washington, Conn., a boarding school for children with special-needs. According to court papers, her lawyers talked to school administrators about putting Emily up for adoption; the school's assistant executive director, Maryann Campbell, and her husband, Fred Cass, expressed interest in adopting Emily.

On December 16, 2004, Christine voluntarily surrendered custody of Emily to Spence-Chapin Services to Families and Children, an adoption agency in New York. On May 18, 2006, Campbell and Cass formally adopted Emily.

According to court papers, neither Campbell nor Cass had any knowledge of the terms of Emily's will or trusts, but eventually they learned that John Svenningsen had arranged to provide for Emily's educational and medical needs. They were sent a letter by Christine's lawyers stating that Emily's trusts totaled $842,397.

But later, they discovered that a federal tax return valued Svenningsen's estate at more than $250 million. The couple sued on behalf of Emily for a new accounting, but Christine claimed that Emily no longer had any rights to the estate since she was re-adopted. The Westchester County Surrogate's Court disagreed, arguing that John Svenningsen meant to provide for all of his children, both biological and adopted.

Although Christine and her biological children appealed, on Feb. 6, 2013, the Appellate Division's Brooklyn-based Second Department ruled in Emily's favor.

"It cannot be overly emphasized that Christine's unilateral surrender of Emily for adoption more than eight years after the decedent and Christine adopted her was not foreseeable at the time the will, and the trust documents were drafted and executed by the decedent," Judge Leonard Austin wrote.

John Svenningsen, he continued, "expressed an intention to include his adopted child in the absence of any reason to believe that his status as the parent of Emily would be terminated by her subsequent adoption many years after his death."

Christine Svenningsen, who has since remarried and has spent about $33 million buying 10 of the so-called Thimble Islands in the Long Island Sound, could not be reached for comment.

Neither Maryann Campbell, nor her lawyer, returned phone calls to ABC News.