Medical problems may have spurred a celebrity real estate agent’s outburst at an assistant accused of killing her over the remarks, the victim’s daughter and the family’s lawyer said.

Linda Stein — who co-managed the storied punk rock band the Ramones before becoming a broker to such clients as Sting and Steven Spielberg — was diagnosed with a brain tumor weeks before she was beaten to death in her Fifth Avenue apartment on October 30, Samantha Stein-Wells and lawyer Eddie Hayes said Saturday.

They said she was taking medicines that sent her on an emotional roller-coaster.

“She had always been prone to mood swings, but the medications and her illness intensified them,” Hayes said. “People who worked with her knew this.”

Police say Stein’s personal assistant, Natavia Lowery, told investigators her boss deluged her with profanities and insults as they worked in the apartment on October 30.

Ms. Lowery told police she lost control when Stein blew marijuana smoke in her face while telling her to hurry in retrieving an email from Stein’s computer.

The assistant then grabbed a yoga stick out of Stein’s hands and used the stretching device to bludgeon her boss in the head and neck, police said.

The 26-year-old Ms. Lowery is being held without bail on a second-degree murder charge. Her lawyer, Gilbert Parris, has said her statements to investigators were made after lengthy questioning and without his presence, although he had told police and prosecutors to notify him.