Tucson, Arizona (CNN) -- Rep. Gabrielle Giffords on Friday left the Tucson, Arizona, hospital where she has been treated since a January 8 gunshot wound, traveling under police escort down streets lined with well-wishers.
She then boarded an aircraft at Davis-Monthan Air Force Base for a flight to Houston, where she is expected to continue her recovery.
Although previous reports had indicated she would move directly to a rehabilitation facility affiliated with Memorial Hermann Hospital in Houston, she will instead be taken to the hospital's trauma center for evaluation and treatment, said Dr. Dong Kim, a neurosurgeon at the hospital.
"She's not quite ready for rehabilitation yet," he said, citing concerns about ongoing medical issues. He declined to elaborate.
The hospital said in a statement that she will be transferred to the rehabilitation facility, TIRR Memorial Hermann, when her health allows.
She was escorted to the Davis-Monthan by a group of motorcyclists from the Veterans of Foreign Wars, according to her office.
She is expected to arrive in Houston about 1:15 p.m. CT. Dr. Peter Rhee, one of the surgeons who has treated Giffords at University Medical Center in Tucson, is accompanying the congresswoman, along with an intensive care nurse.
Also along on the flight are Giffords' husband, U.S. Navy Capt. Mark Kelly, her mother and two congressional staffers.
She'll be flown by helicopter to the hospital.
The move is the latest in a string of milestones for Giffords since the 40-year-old congresswoman was shot in the forehead January 8 in an assassination attempt at a meeting with constituents she was hosting outside a Tucson grocery store.
Six people died and 13 were wounded.
On Thursday, she was able to go outside for the first time since the shooting.
"Today actually, we were glad to say that we were able to take her outside and she was able to do her physical therapy," Rhee told CNN's John King.
"We gave her some fresh air and also gave her some sunshine," said Rhee, speaking from outside University Medical Center. "She was able to see the Arizona mountains."
Giffords' husband described his wife's progress as "remarkable" on Thursday, saying he is hopeful the Arizona congresswoman will make a full recovery.
"I've told her that," Kelly told reporters at University Medical Center. "She recognizes it. ... She is a fighter like nobody else that I know."
Giffords is able to stand with assistance, but is not yet able to take steps or walk, said Rhee, adding therapists are helping Giffords with ways to express her thoughts and, eventually, speak.
"(We are) holding her up so she can train herself to hold her head up," Rhee said. "She is learning to balance and learning all the little things we can take for granted."
On Wednesday, the public learned that Giffords was able to rise from her hospital bed and stand with assistance.
Kelly said he believes she has tried to speak, although she is prevented from doing so by a breathing tube in her neck, and believes she is aware of her surroundings, saying he can look in her eyes and tell. She will smile at him and pat him on the face -- something she did before the shooting, he said.
"Every time I interact with her, there's something quite inspiring," he said.
"We've seen her moving her lips," said Dr. Michael Lemole, chief of neurosurgery at the hospital. But, he said, it's hard to say whether Giffords is actually trying to speak.
But, Lemole cautioned, she has a long road ahead of her that will take months, at least.
Kelly has discussed the shooting incident with Giffords, Rhee said. "She can probably put some of that information together on her own."
Kelly said he believes his wife would be proud of how the Tucson community has reacted to the shootings. "She's going to need to continue to be strong," he said. "She will really appreciate the support of this community."
He said Giffords' family looked at several different rehabilitation facilities and liked Memorial Hermann for several reasons. The medical team there specializes in penetrating head injuries like the one Giffords has suffered, and its closeness to Tucson is also helpful.
Giffords has undergone other "minor procedures" this week, Lemole said, calling it "housekeeping. It's really getting her to a position where she can graduate from this hospital."
Investigators have charged Jared Lee Loughner in the attack. A federal grand jury indicted Loughner on Wednesday on three charges of attempted murder. The indictment charges Loughner, 22, with attempting to kill Giffords and two of her aides, Ron Barber and Pamela Simon.
Legal experts said that more federal charges against Loughner are likely.
Loughner is next set to appear in court on Monday in Phoenix.
"I don't think we're ever going to fully understand the whys and the how and, you know, the reason for what happened on the 8th of January," Kelly told reporters. "It's a loss of innocent life. The injury of a dozen people, the death of a 9-year-old girl, a federal judge and the serious traumatic injury to my wife Gabrielle -- we'll never fully understand that."