Mrs. Kournikova is Regina Kournikova's mother.

Garik Shayk meets Mrs. Kournikova at the Bay City Marathon after he runs from his Tower pursuers. She offers him pizza and something to drink. 

Garik recognizes her when she mentions her daughter, Regina. He also smells cherry blossoms on her and remembers that Regina once said that her mother liked cherry blossom air freshener.

It might seem a small thing for Garik to run into a parent of an old school friend, but the meeting devolves into a disaster for Garik. He's only recently escaped from the Tower's clutches. Mrs. Kournikova recognizes Garik when he calls her by her name, and well, with the Tower on the lookout for Garik, things go downhill from there.

We meet Mrs. Kournikova in Book 4 of The Human-Hybrid Project, Reflections of the Silverback.