I know this from my own life. People tend to people-please too much. You are entitled to set boundaries of your choosing. Altho you might like here, she should respect your wishes. A simple statement without rancor, such as "I termined the study with you for my person reasons. If you can't deliver the magazines without conducting a study, I will stop all contact. I respect you and would like to remain friendly but my wishes must be followed." will probably allow you to remain friendly. Stuffing your annoyance inside and smiling when you want to say enough will cause a scenario where you might become enemies.
As someone said, Friends respect friends. I'm certain that you have accomodated her. She should reciprocate. Are you going to become a full Witness, refuse blood, cut off family and freinds just b/c you like her. How well do you know here?
I've been out for decades. Surely these mags are available online or by just calling Bethel.