The family of the woman at the center of a tragic hospital mix-up following a car crash says she's improving.

Abby Guerra opened her eyes on Sunday, the first time she has done so since the crash and is breathing on her own with the help of oxygen, her family said in a statement posted on the family's website.

The website, www.abbysfightforlife.com, was been set up for donations to Guerra's medical care, and also to provide updates about her condition.

"She still has a long way to go but today was definitely an improvement," Sunday's update read. "Please continue praying for Abby."

For days, the family of Marlena Cantu kept vigil by Guerra's hospital bedside, mistakenly believing their daughter was the one under the bandages, until being told she was the one who had actually died.

"I'm really grateful for the Cantu family because they were at my daughter's side everyday, taking care of her," Maria Guerra, mother of Abby Guerra, told "Good Morning America" today. "I know they're going through a lot of pain because I went through it already. I just want them to be strong and really, give them all the support. ... They were taking care of my daughter."

The funeral for Marlena Cantu is scheduled for today.

Abby Guerra and Marlena Cantu were riding together on a highway in Arizona when they were in a car wreck two weeks ago. Their families were told Guerra was killed in the wreck and Cantu was fighting for her life in critical condition.

After five days of prayer and worry for one family and grieving for another, the hospital gave the families shocking news: There had been a mix-up. Guerra was the one in critical condition. Cantu was dead.

"It's hard to describe," Maria Guerra told reporters Wednesday.

The family had already planned Abby Guerra's funeral.

Maria Guerra said she was repeatedly rebuffed when she tried to see what she thought were her daughter's remains. It was only after an autopsy that was scheduled for Friday of last week that she said officials would allow her to see her daughter the next day.

But before she could do that, Guerra said, officials from the Arizona Department of Public Safety came to her home asking questions about her daughter.

"They didn't tell me anything at that time. ... I don't know what to express but it was really hard to understand what was going on," Guerra said.

Eventually, the officials left, but not before gathering her daughter's toothbrush and retainer, possibly to aid in identification.

Maria Guerra said she didn't find out about the mix-up until at least two hours later when the family was to retrieve their daughter's remains to prepare them for her funeral.

"Despite our daily requests to view the body, we were not permitted to do so for the six days between being notified of her death and the revelation she was alive," Abby's aunt, Dorenda Cisneros, told reporters Wednesday. "If this had occurred, we strongly feel that this horrible situation could have been avoided."

News of Mix-Up Confuses, Causes Anger, Gives Closure

On Monday, the day Guerra was scheduled to be laid to rest, the Department of Public Safety offered an apology.

"Let me send to the families, our sincere apologies from the Department of Public Safety," Sgt. Kevin Wood, spokesperson for the Arizona Department of Public Safety, told Guerra's family Monday, as well as the family of Marlena Cantu.

Officials are reviewing the case because even though the women's injuries were extensive and they looked similar, there were several unique characteristics that could have tipped off hospital staff.

For instance, Cantu was two inches taller than Guerra, still had her wisdom teeth and had a scar on her abdomen from an appendectomy.

"You find yourself thinking: How can this be?" Arthur Caplan of the University of Pennsylvania's Center for Bioethics told ABC News Monday. "We have DNA testing. We have excellent dental records on many people. We have X rays, all kinds of records kept on people. How can it be that we didn't identify someone a week later?"

"We're all angry at the situation," Guerra's cousin told ABC News' affiliate ABC15 after the hospital admitted the mix-up this weekend. "We could have been at her side, telling her to fight. It might have given her more strength."

Guerra, 19, was traveling home from Disneyland in California with four friends when the car in which she was riding blew a tire and rolled over.

Her injuries were so extensive that no one, including visiting friends and family, realized the mix-up.

Abby Guerra Struggling to Survive

"We all went in [to the hospital room]," friend Colleen Donovan told ABC15. "We were talking to Marlena, thinking it was Marlena. Even Abby's parents went in there. Nobody knew."

For Guerra's family, the news of the mix-up ignited several sometimes contradictory emotions.

"Happy, mad, sad, I mean, you can't explain it," Guerra's aunt, Dorenda Cisneros, said. "It's a lot of different stuff."

And for Cantu's family, a little closure.

"It's comforting to know she's not suffering," the girl's father, Frank Cantu, said.

Now, Guerra's family is holding out hope for a recovery as the girl lays in critical condition.

"She's fighting for her life. It's just hour by hour, day by day," Maria Guerra said.

A fund has been set up in Abby Guerra's name. For more information, inquire at any Wells Fargo Bank.