Bandt has the right idea...To quote the Genie from Disney's Alladin, "Tell her the TRUTH!!!"
Once she knows how much you love to tickle her, how it makes you feel, how her laughter is the most beautiful part of her, how lovely she is when she's laughing, how it turns you on and makes you feel closer to her when you touch her in certain areas, how tickling is a part of who you are, your most intimate self, she may come around...
...Or she may not. If that doesn't work, tickle another lady in front of her...a friend of hers, or yours, at a social gathering. You wanna talk jealous??? Things will either heat up or mellow out after you explain, once again, that tickling is not just some fancy you've temporarily taken on, it's who you are, who you were before you met her, and, if nessecary, who you will be once she's passe'...
Sound cold? Such is life, my friend.
Good luck, Ill be rootin' for ya.
Rxx