It really sounds like you are doing all that you have thought about to have a great sex life. I respect that you both make sacrifices for each other and are so inclined to keep a spark in your relationship.
I've never been in a relationship for four years, but I have a couple of suggestions~
This association she has with tickling and fear...try to change that slowly and patiently. Try and find ways that she will enjoy the tickling. I once dated a woman who was extremely ticklish and she didn't particularly hate being tickled, but she didn't particularly like it either--I think because she liked being in control--so the way I got her interested in tickling was to let her tickle me. I am not very ticklish and do not really get aroused from being tickled, but I would lie on the bed with my arms up and she enjoyed making me jolt and squirm. Then I would hold her arms up and give her quick obnoxious kisses in her armpits as she squirmed and laughed.
Next idea, maybe be a bit more creative with your tickling and try different spots. You said it kills her arousal, well try tickling her hips, inner things, knees, back of knees...those erogenous zones. You might just find a spot that turns her on.
And this one I suggest most highly. Since you've been with her for four years, I imagine you know how to get her juices flowing. So after a tickle session, however it goes, follow it up with an intense orgasm.
It does suck that she has this negative association with tickling and you are fighting an uphill battle. But with some good habits you can change that and she will eventually associate being tickled with the hot sex she has with you.
To answer the other part of your question, I haven't heard many tickle stories from women I've been with. I tend to date women who are a bit sullen and timid (it's just my type of lady) so I am often told that they have never been tickled much until they dated me. One woman even told me, on our third date, "I've been tickled more in three dates than I have in 29 years."
