Spritz was a member of a primitive culture who was taken to the Party ship from her planet, Karaknid, by Jenkins, member of the Rulers of the Universe.
She witnessed the murder of Jenkins but did not see the murderer. Correctly assuming that she would be accused of his murder, she disguised herself as a robot waitress and asked for River Song's help. When the real murderer, Marcus Gifford, tried to kill River and Isabella Clerkwell by shutting off oxygen in the room with them, Spritz opened the door saving their lives.
Although River herself believed Spritz, she could not hope to persuade the Rulers of her innocence. Instead, River made the Rulers believe that Spritz was dead and put her on a shuttle, free to see the universe. (AUDIO: I Went to a Marvellous Party)
Later references
While hiding her true identity from the Eighth Doctor, River Song adopted her name. (AUDIO: The Rulers of the Universe)