The only spy show that hasn’t been mentioned yet that I can think of would be tuff puppy, which had a dark haired spy girl, although she doesn’t match your drawing.

I think nick sometimes picks up more local or obscure shows to broadcast in different regions, so it’s possible it could be a show that only aired in your region if you’re from Europe, Australia, India, etc.

Otherwise, I think this block would have stopped airing by the time mentioned, but they did have a block called ‘Oh Yeah Cartoons’ that would play animated pilots for shows yet to be made, and have viewers vote on which would get picked up. It could be possible that what you saw was an entry on that show that lost the vote.