Girlfriend Anal

Me and this girl have been seeing eachother for months and she really wants to try anal. I spent like 100 on anal toys, beads, use silicone lube everytime. I had my whole cock in her ass. She was completely lubed up ( silicone lube) brought out a toy while I licked her ass, but still can't get her to loosen up enough so it doesn't hurt her. She gets really apprehensive then it tightens up. Any help?