A 42-year-old Eden Prairie woman has admitted to feeding her need to shop by embezzling more than $1.2 million while working for a Golden Valley property management company owned by her mother, in the largest embezzlement case ever prosecuted by the Hennepin County attorney’s office.

Stephanie L. Castillo pleaded guilty Monday to theft by swindle and is expected to receive a sentence of six years and eight months, according to County Attorney Mike Freeman.

In the meantime, the death of Castillo’s 12-week-old boy in mid-July remains under investigation by Eden Prairie police, a department spokeswoman said Tuesday. Suspicions surfaced when an emergency room doctor at Fairview Southdale Hospital in Edina found it unsettling that Castillo asked about receiving insurance benefits 20 minutes after Leo died, according to a search warrant affidavit filed in Hennepin County court. Castillo has not been charged in the case.

When approached by police in October regarding the financial allegations, Castillo confessed to stealing $1.2 million while vice president of Balderson Management, Freeman said half of the money was burned away on shopping and the rest funded her husband’s effort to start a business in Cabo San Lucas, a resort city on the southern tip of Mexico’s Baja California peninsula.

The dollar amount in her case tops that in another prominent embezzlement case, that of Joel Pourier, executive director of the Heart of the Earth charter school in Minneapolis, who in 2010 received a 10-year sentence for embezzling more than $1 million.

Castillo was accused of embezzling money from four companies, starting in 2009, while working at Balderson. Cynthia Balderson ran the daily operations of commercial properties, and Castillo provided property management and leasing services.

Castillo had access to clients’ funds and drafted fake invoices for vendor services and applied some of the payments to Balderson’s records, the charges say.

The final step was creating hundreds of fraudulent checks and forging her mother’s signature. Castillo made most of the checks payable to herself, but also used her clients’ businesses’ checks to pay personal bills, prosecutors alleged.

In October, Richard Martens, co-owner of commercial properties managed by Balderson, discovered the theft after realizing his “business projections were coming up very short.” After auditing his financial records, he noticed that several check amounts didn’t make sense. He then concluded that check signatures were forged and notified police.

Once confronted with the evidence, Castillo told investigators that the thefts started when she was desperate for money to help treat her ailing dog.

As for the death of Castillo’s 12-week-old son, Eden Prairie’s police investigation remains open, according to department spokeswoman Lorenz.

The Hennepin County medical examiner’s office said Tuesday that it has ruled Leo’s death as “undetermined” and closed its investigation.

Lorenz said police had “not received the ME’s official report yet, and our investigator is still working on the case. I’m guessing the toxicology tests we’re waiting on are unrelated to the autopsy.”

According to the search warrant affidavit, Castillo drove her son to the hospital about 8 a.m. on July 18. He was unresponsive when she arrived, and she told doctors she had found him in that state in his crib. Her 3-year-old son was next to Leo in the crib, she said.

The boy died about 40 minutes after being brought to the hospital. The doctor said Castillo was “appropriately upset,” but 20 minutes later asked how soon death benefits would be paid, the document said. The doctor consulted with her primary physician and learned that Castillo was the subject of a pending criminal case for embezzlement.