It heavily depends on everyone's age involved. Many younger women might have a problem with it. It also depends on the comfort factor of everyone, and your relationship with your woman. Some insecure women might have a problem with it, but it your relationship is strong, it shouldn't matter. Probably makes a difference if her sister is nice looking as well. If her sister is busted (bad looking), there shouldn't be any worries.
Now if this was how I give a foot massage, it might start problems. I am known to rock a good one.