I think you should continue to stress to your friend, that you do not wish to continue giving and receiving presents, but would rather just celebrate with a lunch. I know you have already tried this and it has fallen on "deaf ears" but having had a similar experience with friends, and one in particular who just did not want to "give it up", I just kept repeating it, making sure that when a birthday or Christmas giving was coming up to firmly remind her, NO GIFTS. Unfortunately, the thing that finally convinced her I meant it was I did not give her a present but asked her to lunch only. She finally got the message when I brought no present. I told her how much I valued just spending time with her, that this was our presents to each other. I think it is possible she may "seem" offended for awhile, but if you are true friends, it is not going to change the friendship except maybe for the better.