I always look at situations like this with an eye on how they analog into a more vanilla sexual context.
To you Tickling is much like a favored sex position, that works better for you to get off in. I've spoken to enough guys who favor on position over all others for assured orgasm. Tickling for you plays a similar roll in your sexuality, you don't need it to get off, but if you can add it in things go oh so much better, right?
Looking at it like that, then of course you'd tell your partner. You'd communicate a position that worked better for you sexually, because you'd want them to know what works for you, and why. It's not going to be something that you do EVERY time, but it is something that makes your sexual experience better, and the person you are sharing said sex with deserves to be in on the facts. You want her to enjoy your times together, and she wants the same for you.
It's understandable that you have honest fears about sharing this aspect of your sexuality with her. That natural state for most paraphiliacs is to hold some shame over their like. It's a sadly natural result from simply existing in our culture, which is one that is conformist by nature. We learn early on that different is not liked. So we hide.
The difference here is that you seem to be forming a significant relationship with your partner, one that has a potential for the long run. And if that is indeed the case, then allowing her to see the whole you, your whole sexuality, is the right thing to do. She deserves the chance to know what her possible future partner needs regarding his sexual happiness, so she can know if she can provide it. (and not accidentally exclude it without knowing)
Best of luck. It sounds as if you have little to worry about, given your current inclusion of tickling already with no rejection. She may not "Know' but on some level I wager she understand that there is something in it that works for you.
Myriads