The actress' mother has been accused of physically and emotionally abusing the 14-year-old, which prompted a judge to temporarily strip her of custody in early October. An initial report by child protective services found evidence of emotional abuse but claims of physical abuse were deemed inconclusive, Superior Court Judge Michael Levanas said last month.
Chrisoula "Chrystal" Workman denies she has ever abused the actress. She claims her other daughter, Shanelle Gray, is not a fit guardian. She contends Ariel is a rebellious teen and should be returned to her home.
Levanas will hear testimony and consider multiple factors during the trial, which is expected to last several days and won't be fully resolved before the new year.
Ariel turns 15 in January, and Levanas will likely consider her views during the trial. She has not yet appeared in open court, although she was rushed to a Los Angeles courthouse from the "Modern Family" set in early October when Gray filed for an emergency guardianship.
Since then, she has been living with Gray, an actress who has appeared on "The Bold and the Beautiful" and operates acting studios with her husband. Gray's attorney has said she was subjected to similar abuse by her mother and that state authorities removed her from Workman's home when she was a teenager.
Ariel, who has been acting since age 7, plays Alex Dunphy on the ABC series, which is both popular and critically acclaimed.
Guardianship cases in California are public record. Gray's attorneys requested the case and its proceedings be sealed, but a judge refused. The case was filed under Ariel's birth name, Ariel Workman, in part to avoid attention.
Although The Associated Press does not generally name underage victims of abuse, Ariel's name is being used because it is included in the public guardianship case.
Workman has said she would undergo counseling and take other steps to regain custody of her daughter. Her attorneys have been given some details about Gray's finances to try to bolster their argument that she cannot adequately support Ariel.
Workman has claimed Gray wants to use Winter to foster her own acting career, but Gray's attorney Michael Kretzmer denies that.
"Shanelle is successful and has done very well in her own rights," Kretzmer said in an interview last month. "This is a tragedy for her, too."
Workman has filed more than two dozen declarations from friends, neighbors, stylists and others who say they have never seen her abuse her daughter in any way.
Kretzmer told a judge in October that people on the "Modern Family" set have expressed concerns about Workman's behavior and her daughter's wellbeing.
"A controlling mother does not mean she's unfit," her attorney, Anita Gumm, said at a hearing last month.
Another of Workman's attorneys, Nick Pacheco, filed a defamation lawsuit Monday against an actor who teaches at Gray's studio for allegedly calling his client "an abusive monster" in an online post.
Levanas will not handle that case, but will have to consider a proposal by Ariel's father to care for her.
Glenn Workman is estranged from his wife but states he would be willing to care for his daughter if Levanas approves. The judge initially rejected his request, citing inconsistent statements Glenn Workman made in court filings and to child protective services investigators.
Ariel's money isn't an issue in the case yet. Levanas has not granted Gray any control over the actress' earnings, a portion of which are automatically deposited into a special account meant to protect child actors.
She has several projects in the works and already has a lengthy resume of appearances on TV series such as "ER" and "Phineas and Ferb" and movies such as "Kiss Kiss Bang Bang," ''Ice Age: The Meltdown" and "ParaNorman."