Office Politics

Ok in order to recognize birthdays, holidays and events, our department has created an "Event Fund." The Event fund is $2 per person each month. The cost covers treats, cards, decorations, napkins, forks or what else may be needed for the celebration. The department has about 20 people in it and all but 4 people participates. The rules are simple: "You have to pay to play!" Out of the 4 people, 2 do not participate because of religious preferences-respected and understood. One person participates and pays according to the events that is being celebrated i.e. St. Patrick's Day, Valentine Day, Halloween as long as it is not religious based-respected and understood. The last person does not want to pay but wants to participate. For the last past 4 years this person has not paid but taken part or eaten. Why? When questioned, she states that she has not made up her mind as of yet (keep in mind she is eating a piece of cake as she responds)! In a polite manner, I explain that the cake is for the participants and if she chooses not to "pay up" then do not "eat up." She responds,"It does not matter anyway because you will just trash it anyway." Before she rudely cuts me off, I attempt to explain the rationale behind the Event Fund but she refuses to hear it. In order to maintain composure, I step away from the area for a few minutes. When I return, I have a note stating, "Here is $2 dollar for the piece of cake." Oh yeah the $2 was in all pennies. So as I do everyone else who pays, I wrote her out a receipt. My question is why do people think they can free load on other people? It is not about the $2 but the rationale behind it!!! Now this person refuses to speak or even acknowledge me. What did I do wrong? One co-worker states that no one ever said anything because they did not want the confrontation. Should I inform the manager of what transpired in case this situation turns into a disaster? I enjoy my job and do not want to feel uncomfortable at work or make anyone feel uncomfortable. I just want to do the right thing. Any feedback?