As a muslim, when I am at a church service, either at christmas or when someone has passed away, I say muslim prayers at the same time the vicar or minister leads the congregation in a christian prayer. I say my prayers in the same manner as the congregation says theirs. So, if they kneel to pray, I do too.
GUW is right. Only a muslim woman who chooses to cover her head, upper body or entire body would do so in church as she would in most public places. Most muslim women I know don't cover themselves (with a hijab, chador or burka that is) in public so they would attend church "as is".