Windblade, Chromia, and Arcee were already getting toys when Nautica was introduced. She was made-up by the folks creating the comics to be an additional girl. She was never meant to get a toy at the time, she was just another comics-only character like Pharma and Rung.
I am aware that it doesn't attach to the torso. But being attached to the torso does not prevent a hat from falling off. In real life, a traditionally-cowled Batgirl could easily uncowl herself just by turning her friggin' head. This design actually solves that problem, as the cowl is anchored to the part of the body that it should be staying on -- the scalp, rather than the neck. If New Batgirl's cowl is in danger of coming off all the time, then so is Batman's. Being connected to the torso gives the illusion of security, but actually offers very little. If the cowl isn't snug against the head, it's going to come off during heavy movement, same as any hood.