Debra Opri wants to force binding arbitration under the terms of a contract in which she agreed to represent Birkhead in September, according to the lawsuit filed Tuesday in Superior Court.
Opri said her work on Birkhead's behalf was "extensive, entailed hundreds of hours of work" and required her to travel to multiple states and outside the country. The lawsuit did not specify a dollar amount.
After-hours phone messages left for Opri's attorney, David Owen, and Birkhead's lawyer, Michael Whalen, were not immediately returned.
Birkhead sued Smith in October seeking a paternity test of her daughter, Dannielynn Hope, to determine who was the baby's father.
Howard Stern, Smith's attorney and longtime companion, had also claimed to be the father and was listed on the baby's birth certificate.
A Los Angeles judge ruled in Birkhead's favor in December but the DNA testing was not performed until months later. Smith died in Florida on Feb. 8 of an accidental overdose of prescription drugs.
After a highly publicized court dispute, paternity tests released last month showed Birkhead was the baby's father.
Opri was Birkhead's attorney during most of the dispute but later withdrew from the case without explaining why.