I wouldn't push the issue on this. If she isn't offering forget about it.
Imagine you met a girl and found out her ex bf had pictures of her naked and used them as blackmail and stuff. You wouldn't be happy. Do you have a sister? Do you want her BF having nude pics of her?
I'd cut the shit and watch porn. Keep it up and you'll find yourself dumped.
On a related note it is EXTREMELY easy to get a girl to make a porno with you if you offer to do it on her phone/camera and make sure you don't ask for a copy for yourself. Just let them be comfortable and not regret doing it since they are the ones who possess the video and usually they'll eventually offer to send you a copy.
I have yet to get turned down when I suggest it because I specifically make the point that I don't want a copy for myself since I don't want them to regret it and get all upset and shit like girls sometimes do.