56-year-old Lois Reiss's appeared before a magistrate judge in South Padre Island.
She is suspected of having transferred funds from her disabled 61-year-old sister's account to her own and then withdrawing them at the casino.
The Dodge County Sheriff's Office said Friday that investigators from Minnesota and Florida traveled to Texas to process the stolen vehicle.
Authorities said that Riess (left) fatally shot Pamela Hutchinson, 59, in Florida, after befriending her.
"He asked her how many people and she said, 'Oh, no, I'm just looking at the menu, ' and I'm looking at it and I go, 'I know this lady, '" said George Higgenbottom, manager of the restaurant Dirty Al's.
It's unclear when she will answer to criminal charges in Minnesota.
Officials say Riess had spent the day, after allegedly killing her husband, at the Diamond Jo Casino in Northwood, Iowa. She will be extradited to the state that arrives first. Investigators believe Riess used the same gun to kill Hutchinson and her husband.
Surveillance video released over the weekend captured her final hours of freedom. South Padre Island, where Riess was apprehended, is three miles from the Mexican border.
Riess was waiting in a Texas jail prior to the hearing.