Depends, really, upon how well you know each other... are you friends already, enough so you'd get away with the tickles, or is this someone that you WANT to get to know better so that you can tickle her? If she's already a friend, that opens up a bunch of avenues for you to pursue, but if this is someone who could be freaked out by some guy she barely knows reachin' out and getting her, I'd advise caution. (especially in this day and age)
First thing that came to mind when I read this, though, was this;
You're there talking to each other, and you look at her belly and say something like, "What's that on your tummy?", as you're reaching in for the tickle. That way they're a little distracted, like you've just looked past them and said "What's that?" or at their shoes and told them they're untied. They're instinctively gonna look, and you can be in motion before it registers that you're gonna get them. Then, before they know it, you're tickling. Voila! And maybe, if this is the first time you've tickled them, you might be lucky enough to find it well-recieved, and it could open the way to future tickles! Yay!
Or, you could get your ass handed to you. 🙄
Either way, let us know, hmmm? 😉