Dr. Kal Sharma will examine Dawnette Knight, 32, in jail, where she is being held on $1 million bail.
Sharma must report back by Sept. 15 on whether she is competent and able to aid her attorney, Superior Court Judge John Riley Jr. said.
"That's a matter that requires a physician's opinion to determine your state of mind," the judge told Knight.
Knight wasJune 3 at her Beverly Hills apartment. She is charged with one felony count of stalking and 24 felony counts of making criminal threats. If convicted, she could face up to 19 years in state prison.
The charges involved more than two-dozen letters that were mainly sent to Zeta-Jones' husband, actor Michael Douglas.
"We are going to slice her up like meat on a bone and feed her to the dogs," said one letter read in court by Zeta-Jones last month when she testified during a preliminary hearing to determine whether there is enough evidence to put Knight on trial.
Knight has apologized in a letter that claimed she had been infatuated with Douglas.
Defense attorney Richard Herman said his client was never a threat and never should have been arrested. Instead, he said, authorities should have simply profiled and taken note of her.
"This was botched security. This was a botched investigation," he said.
The defense attorney said he believed his client would be found competent to stand trial and that if convicted, she should receive probation and counseling rather than any prison time.
"I don't think it's mental illness. It may be obsession," Herman said.
Herman acknowledged that his client had at least two previous arrests. Although he did not have details, Herman said she was arrested for allegedly filing a false report after she recanted a contention that an ex-boyfriend abused her. But he said it is not unusual for women in such situations to recant.
He also said a "neighborhood squabble" led to her being ordered to perform community service, apparently for assault, in a Florida case, but nobody was injured.
Calling her "a perfectly normal woman," Herman said that, if convicted, Knight should receive probation and counseling rather than prison time.
"There is no serious criminal record. ... There is no history of her ever harming a human being," he said.
"Put her in a program somewhere where she gets fixed," he said.
The preliminary hearing was suspended last month whenafter an incident in which he suspected his client attempted suicide.
Knight was too drowsy for a court session in July and told her attorney she had taken sleeping pills, Herman said, but he suspected she tried to overdose on barbiturates.
Outside court, Herman repeated allegations that Zeta-Jones had driven his client to attempt suicide by orchestrating a media campaign against Knight.
"It's being waged by Zeta-Jones with her knowledge and it's abusive," Herman said. "... It's an abuse of her position and her power."
District attorney's spokeswoman Sandi Gibbons said the issue should be the alleged crimes and not "some sort of mythical suppositions from her attorney."
"We have evidence that she committed very serious crimes and we intend to continue with this prosecution," Gibbons said.
By Robert Jablon