When you reach a certain age you get tired of doing stuff because you have to. When I was in my 20's I would have felt the same way as you do - that I should go or it would seem rude. Now that I'm 41, I feel a whole lot different. Just tell your neighbor thanks for the invite but no thanks, you used to belong to that church and have no inclination to join again. You really don't owe her any explanation. I'm a big believer of being on good terms with my neighbors, but I don't have to be best friends with all of them.