(CNN) -- The family of American student Amanda Knox is happy that new DNA analysis has called into question her murder conviction, but won't celebrate "until she walks out of that prison," her mother said Thursday.
In an interview with CNN's "Newsroom," Edda Mellas said her daughter is "not taking anything for granted." But a priest who was visiting Knox reported the results were met with "jumping and hugging" on Wednesday.
"There are many people that support her," Mellas said. "He said he could finally see the light back in her eyes, and she looked like she could finally breathe after three and a half years."
Knox and her ex-boyfriend, Raffaele Sollecito, were found guilty in the 2007 killing of Knox's roommate, Meredith Kercher. Kercher was found dead in the villa she rented with Knox in the central Italian university town of Perugia, semi-naked and with her throat slashed.
In December, Knox was sentenced to 26 years in prison. But Wednesday, forensic experts told an Italian court that the DNA evidence police used to link Knox to the murder weapon may have been tainted.
The next hearing in her appeal is scheduled for July 25, with further hearings on July 30 and August 1. Mellas said a decision on the appeal could come in late September.
She said her daughter was "a naive, idealistic, easygoing 20-year-old" when she was arrested, but has "gone into her own little shell" while in jail.
"She's definitely grown up," Mellas said. "She's had to learn how to survive and take care of herself. She has become much more closed in that environment in order to kind of survive."
At the trial, prosecutors said a knife found in Sollecito's home had traces of Knox's genetic material on the handle and Kercher's in a tiny groove on the blade. Investigators also traced DNA on Kercher's bra to Sollecito.
But in a 146-page report, forensic science professors Carla Vecchiotti and Stefano Conti concluded that while Knox's DNA was present on the knife handle, tests for Kercher's DNA were unreliable.
"There is no conclusive scientific evidence regarding the nature of the blood," the their report states. It added, "It cannot be excluded that the result obtained from sampling the find B (knife blade) could be the result of contamination" occurring at any stage of the testing process.
Investigators did not follow "international inspection procedures and protocols for gathering and presenting evidence" in testing either the knife or the bra fastening," they found.
Prosecutors say the knife had been used to stab Kercher in the neck and that it had been cleaned. The DNA matter attributed to Kercher consists of flesh, not blood, they say. But the sample was so small that forensic scientists investigating Kercher's slaying were unable to double-test it in accordance with international forensic science norms, which Knox's legal team says raises doubts about its validity.
Defense lawyers also say the tiny metal clasp from Kercher's bra, which was cut from her body after her murder, may have been contaminated because it was not collected as evidence until nearly six weeks later.
In an appeal hearing Monday, Knox took to the stand herself following testimony from a third person convicted in the case, Rudy Guede. It was the first time the three defendants had appeared in court together since a preliminary hearing years ago.
Guede, who was found guilty of murder in a separate fast-track trial and sentenced to 16 years, refused to say Knox was not involved in the killing. A prosecutor then read out a letter sent by Guede in 2010 in which he said he thought the American and her then-boyfriend had killed Kercher.
An emotional Knox responded, saying: "The only time that Rudy Guede, Raffaele Sollecito and I were in one room together was in a court room.... He knows what the truth is. I don't know what happened that night."
Journalist Livia Borghese contributed to this report.