[Rusty's Momma]

If you only broke one pane (meaning not all the way through) then only that one side of glass should have to be replaced. They will reseal it.
Measure that section of the window and tomorrow morning call around to some glass/window repair companies and give them the measurements. Tell them whether it is just one pane or both and you need an estimate to repair.
It will be ok... as long as you are willing to repait it she shouldnt be to upset with you if she is a good friend. It isnt like you are tying to hide it or not disclose to her that you broke it.
Keep smiling.. it will be ok