With my girlfriend I always just playfull tickled her then wen I actually said "I like tickling you" she said "well duhh!" lol, now I get to tickle her every now and again although shes not fond of it. Usually we'll make deals like she's trying to quite smoking so if she buys a pack it's costs her an hour of tickling. And other things but you get it. Point is if she loves u she'll understand. Try givig her a foot rub and kissing her foot see how she reacts. Not gonna lie sex could help you here especially if she wants it. Start kissing her feet in a romantic way and work your way up you know? Girls like sex as much as guys so if you give her what she wants you got a better shot at getting what you want. 
And if you do get what you want don't always obses with her feet. Remember theres a woman attached to em 😛