Anthony, 22, was arrested last week after reporting the disappearance of her daughter Caylee Marie Anthony. Casey was charged with child neglect and criminal obstruction for lying to detectives.
Casey's mother Cindy Anthony said Monday on NBC's "Today" that Casey should be released from jail so she can help with the investigation.
"I know Casey knows who has her," Cindy Anthony told NBC. "I know Casey doesn't know where they're at right at the moment. But I don't know anything else right now because I can't speak to my daughter. And we're trying to get that changed very quickly."
Casey's lawyer, Jose Baez, said his client wants to cooperate with authorities.
"She is a good mother and has no history of being a bad mother," Baez told a news conference Monday. "She wants to find her daughter."
Sheriff's officials have said they doubted statements the mother made that she had dropped the child off with a baby sitter last month and had not seen her since.
Casey Anthony allegedly asked a neighbor to borrow a shovel around the time Caylee went missing, deputies said. That was June 9, according to detectives.
They said Anthony contacted police because her mother was concerned.
Authorities said Casey Anthony has repeatedly lied to investigators and showed little emotion during interviews about her daughter's whereabouts.
"She didn't seem to be concerned," Orange County Deputy Sheriff Carlos Padilla told ABC's "Good Morning America" on Monday. Padilla didn't return calls from The Associated Press on Monday.
Last week, sheriff's investigators used cadaver-sniffing dogs and dug through Cindy Anthony's backyard to look for Caylee.
Anthony didn't call authorities immediately, she said, because she was conducting her own investigation, according to the charging affidavit. The apartment where she allegedly dropped off the girl hadn't been occupied in months and Anthony gave detectives a bogus employer, manager's name and work telephone number, according to the affidavit.
Casey, who is being held without bail, is scheduled to appear in court Tuesday.
