A woman charged in the arson death of a mentally retarded woman in her care will undergo testing to determine whether she is competent to stand trial.

Second Circuit Judge Alfred C. VanWagenen on Thursday rescheduled a preliminary hearing for Tonya Vosburgh and her husband, John Vosburgh, for Jan. 20. The Vosburghs, formerly of Layton, are charged with murder, aggravated arson and filing a false insurance claim.They are accused of setting the fire at their Layton home that killed 18-year-old Bobbi Jo Womack, whom the couple cared for under an agreement with Womack's mother.

The defense claims Tonya Vosburgh injured her head when she fell on a sidewalk in July. That injury reportedly resulted in an aneurysm that required brain surgery on Aug. 4.

Since then, according to court documents, the 33-year-old woman has suffered an organic brain disorder and seizures that have resulted in hospitalizations.

Other court records filed by her attorney, Randall Gaither, state that a stroke has cost Tonya Vosburgh the use of her arms, some of her ability to speak and some of her memory.

"Tonya Vosburgh is mentally unable to conduct her own affairs, to care for herself and now requires long-term nursing care," Rick Vosburgh, 43, filed a petition with the district court asking to be appointed his wife's conservator. A hearing on the matter is set for Dec. 2.