The 44-year-old Welch is engaged to McClusky, who was serving a 15-year sentence for second-degreee murder before he and two other inmates escaped from an Arizona prison last Friday.
"She aided and abetted in the escape of convicted felons," Charles Ryan from the Arizona Department of Corrections said of Welch.
It all began when McClusky, Province and a third convict, Daniel Renwick, cut through the fence of a medium-security prison on Friday. The prison is located in Kingman, Arizona.
Shortly after their escape, the convicts kidnapped two big-rig drivers at gunpoint and demanded to be taken to Flagstaff, Ariz. The drivers were later released unharmed.
Province, 42, was serving a life sentence for murder and robbery. Renwick, 36, was serving a 22-year sentence for second-degree murder.
Renwick made it all the way to Rifle, Colorado before a Sunday morning shootout led to his capture. Renwick, now back behind bars, is being questioned by the FBI.
Private Prisons Mean Lax Security?
While authorities from several agencies continue their hunt for McClusky and Province, officials with the Department of Corrections are scrambling to tighten security at the Kingman prison. Officials blamed the escape on a combination of lax guards and a failed alarm system.
An alarm failed, they said, on the door that the inmates passed through. Although a second alarm sounded when the inmates cut through the fence, guards apparently failed to notice.
The Kingman prison is operated by a private Utah company. The security failure has fired up debate over whether states should outsource prison operations to save money. Thirty-two states already do it, but critics say private guards often receive inferior training and pay.
"My concern is the staff at this prison may have been lax in their job and that probably created the opportunity so that they could escape," Ryan said.
Prison Break: Inmates 'Armed and Dangerous'
In a bad economy, proponents argue that private prisons make sense for taxpayers.
"Arizona is facing a multi-billion dollar shortfall," Arizona State Representative John Kavanagh said. "We have to find savings wherever we can and corrections is a big part of our budget."
The company that runs the Kingman prison did not return phone calls from ABC News, but Arizona officials said the firm will have many questions to answer soon.
Escaped Convicts Still In Arizona
Meanwhile, Province and McCluskey have not strayed far from the medium-security prison, police said.
"It is thought that they are still in the region, in Arizona," Ryan said.
Police have said they were no longer looking for a 2002 silver Volkswagen Jetta that they believed the prisoners may have bought off Craigslist, but gave no explanation.
Province, McClusky and Welch were last spotted in Phoenix Saturday, withdrawing money from ATMs.
"Hopefully, they'll surrender, and their families will talk to them and give them good advice," Chief Deputy U.S. Marshall Fidencio Rivera said. "We don't want anybody to get hurt."
One local woman said, "I'm sure they will be caught, but in the meantime, I think everyone needs to be warned."
The Associated Press contributed to this story.