Ponko is one of the human-like combat droids used in the war, who was repurposed into a maidbot when it came to a close. Her model has been banned after the war it seems, hence why she's a rarity.
@Oured The carpenter guy in the previous chapter said production for humanoid models stopped when he was a kid. Not just for Ponko's line, but all of them. I agree it's likely she was originally a combat model, though.