Britney Spears spent more than two hours at the Los Angeles office of Kevin Federline’s lawyer, Mark Vincent Kaplan, Monday for an ongoing deposition in the ex-couple’s custody battle.

At 10:40 a.m., Spears, 26, wearing a dark blue top and jeans, drove up to the office in her white Mercedes-Benz SL65 with friend Sam Lutfi. Both had serious expressions on their faces. The singer was spotted leaving at 1:20 p.m.

The singer has missed numerous appointments for the court-ordered cross examination. She was expected to be grilled about her past drug and alcohol use, her apparent failure to follow court orders and other matters pertaining to her parenting skills.

Federline’s attorney will use evidence gathered in depositions to try to convince a court that his client should retain primary physical custody of the ex-couple’s children. A custody trial is set for April.

“Kevin wants nothing more than to be able to parent his children with participation by their mother,” Kaplan previously told PEOPLE. “But the best interest of the children require that they be in the most sound, safe, nurturing and consistent environment. That is paramount.”