In this challenge by a foster parent to an order placing children in Mexico with their father, the issues are (1) whether the parental presumption applies in a suit to modify child custody and (2) whether the trial court abused its discretion by determining the children's best interest was served by ordering them to live in Mexico with their father. Initially the children were placed with Blevins in foster care after the Department of Family Protective Services took custody following both parents' drug use and neglect. The mother eventually terminated her parental rights and the father, after a prison term, was deported to Mexico. After a hearing and home study, the trial court ordered the father to have supervised possession of the children in Mexico. That home study found the father living with brothers in an unfurnished house -- and uninhabitable, according to Mexican authorities -- and the maternal grandparents' home only large enough for them. Blevins, the foster parent, sued to be named the children's sole managing conservator. The department then petitioned to modify the children's custody, to name the father and maternal grandmother as joint managing conservators. The trial court ordered the children to be sent to Mexico to live with their maternal grandmother. Seeking mandamus relief, Blevins sued to stop the trial court's order. The court of appeals denied her mandamus petition.