Girlfriend likes toe sucking, foot .. GIRLS ONLY PLEASE?

I am very turned on by my gf's feet, and the first time i got the courage to suck her toes, she absolutely loved it, to my surprise, and got very very horny, we sucked each others toes for 30 minutes then had amazing . she told me the second time that i did it that it was very pleasurable for her, but sometimes she seems shy when I try to kiss her foot and gives me a strange look, so I haven't tried sucking her toes again.. how should i approach it, and, girls, do you like it when a guy sucks your toes?