How about adding "C:/Program Files (x86)/Git/bin" to your windows %PATH% and removing the customization for vc-git-program? Then plain "git" will find the right executable, no matter locally and remotely. That's what I do. (You'll have to restart emacs after changing %PATH%.)
I like to set my windows env using the GUI under the System Control Panel, but there's other ways to do it, search the web if you need help with that.