How do I ask to touch my cousins feet?

I rarely see my cousin now because she graduated high school last year but once in awhile she comes around and I see her. Im 15 and shes 19. she has beautiful feet, and she used to be kinda heavy, but now lost a lot of weight and i have become kinda attracted to her. she came over friday night to sleep over and hang out with me and my sis. my parents werent home. she kept putting her feet on me and saying let me put them on you! but i refused to hide my fetish. getting aroused by the who thing secretly, it was arond 11 at night and my sister had fallen asleep and so had my cousin on the couch in her sweaty black socks. i snuck on to the end of the couch by her feet and slowly took the blanket of them and rubbed her toes. i jacked as i did it, it was amazing. but she left early tht morning to goto work and i slept in. havnt seen her since and i keep thinking about tht wonderful night. next time i see her, how can i ask to touch her barefeet...like not in a creepy way. its a fetish i cant help it