Who is Antonina Pavlovna Platoshkina from We the Living and what is their importance?

Antonina Pavlovna Platoshkina is a wealthy woman, who is in the sanatorium with Leo. She later looks him up after returning to the city. Antonina helps make the connection between Leo and Karp, and the two men form a smuggling operation. When their operation is about to be investigated by the Communist police, Tonia reminds Leo that he must remember she has nothing to do with it. When Leo is released from jail, Tonia offers him money to go away with her and he accepts.