I mean, it's really tough to say anything in this situation. Way too many unanswered variables. Are you sure they were looking at her feet? Why do you think they were looking? Do you think it was from a fetish standpoint or just a random look? Sometimes people just look at other people's feet with absolutely no intention behind it. If someone is barefoot around other people, at least one person is hypothetically going to look at the feet. Have your friends ever given or shown any signs of having a foot or tickle fetish?
Also, I feel like that's the point of taking care of your feet and getting pedicures. I mean, sure, some people do it to feel good about themselves or enjoy the process, but if your wife gets pedicures or takes care of her feet and then goes barefoot, I mean somewhere deep down inside maybe there's the subconscious impulse that said person is making their feet nice so others will see them looking nice? Just a thought.