I hate to be a wet blanket, but I think you're screwed. Once you let it all "hang out" like that and she responds with a less than sterling reaction, I figure that anything you do to her that is tickle related will freak her out.
Think about it this way: Because our fetish is so "abnormal" most people will see it as really strange. Suppose that you had a friend that told you that they got their rocks off by humping peoples legs like a dog. though this sounds extreme, to all outsiders of our fetish, it pretty much sounds the same.
From this point forward, your friend is going to know that tickling her turns you on. Mix the wierdness factor with the fact that she knows that you are doing the tickling equivalent of feeling her up, and you have a recipe for disaster.
But, what do I know. Maybe she'll get used to it and allow you to in the near future.