Francesca only thinks she's a robot.
She apparently has blood, she definitely breathes, and (since we don't see her insides or schematics) we only have her word to go on. It's entirely possible that she suffers from schizophrenia or some other mental illness, especially since she exhibits signs of instability at times.
Speculatively, she's a foundling that Baron von Frankenstein found washed up on his island one day, and when he talks about how she was his greatest creation, he means that he raised her well. Her delusion about being a robot may be something he regards as a harmless personality quirk, considering his different perspective and moral sense.
Since the other monsters don't meet up with him that often, they think he actually created her.
- On the other hand, she may be an artificial lifeform like The Frankenstein Monster, who is treated like a robot throughout the picture, such as having a metallic clank to his foot when Dracula tries to kick it.
