That fact that she wants you "tickle" her feet means it's definitely more than the actual sensation. She wants you to pleasure her feet with touch, but the parameters have not been established for maximum effect. I call it the "scene." Usually, ticklers are bigger on this than ticklees. They prefer a scene, or setup for their fetish, e.g. bondage, bare/nylons, nude/clothed. Ticklees I've known who have a preferred scene often focus on the tickler getting inside their head, with taunts, or a blindfold to boost the anxiety quotient. They sound like small details, but they are very important to many ticklers and ticklees. If you can narrow down the elements of her ideal "scene," a mere pinky finger up her sole will become electrifying. Bottom line: it's not always just about the actual act of tickling.