There's a math error even assuming your premise is true. There are 3.75 billion women on this world. Even limiting it to women with smartphones, there are over a billion of them. If each of them is currently spending $0.50 on a notepad (again, we're assuming your premise is true even though it's not), that's a $500M market. Not bad.
It's recurring revenue also. Eventually all of them will run out of space in the notepad and have to buy a new one. It might take years if you assume a page a month but maybe with clever marketing you can get some percentage of users to upgrade to luxury $5 notepads. That's 10x revenue per user!
