Go for it
Since you have a great opportunity it would be best not to waste it. There are two steps to this process.
First I would run my finger along her soft sole. She will either giggle with delight or kick out in protest. If she giggles with delight then they have extended and invitation to continue. In that case I would grab one of her feet and tickle it. If she is in a playful mood at that point her soles would be tickled, her tops would be kissed and her toes would be gently sucked. All done while she continues to giggle and laugh.
On the other hand if she kicks out in protest there is still hope. I would offer up a quick apology. Something like, "Sorry, I couldn't resist" Then I would politely say, "Since you didn't like that, I probably shouldn't do this..." At that point I would grab her foot and tickle it gently. I would ignore her protests for a few minutes and continue to tickle her. Of course I know I would have to stop tickling her so as not to piss her off too much, but I would enjoy every second of the ride. 😉