Usually this type of behavior isn't socially acceptable to someone you first met but if you think that she feels comfortable around you and is open to that kind of thing, then I don't see why not. I only say that it's usually not socially acceptable because massages seem to be rather intimate and most people don't like others getting into their personal space unless they are comfortable. But if for whatever reason the two of you have hit things off really well and are totally comfortable being around each other, I don't think that it would hurt to ask if she would like one. If she says no, then just shrug it off as if it were no big deal but if she says yes, then you can go ahead and massage her foot or whatever.