I'm going to exclude my friend from my wedding because she won't exercise
That's an unusual reason to exclude someone from a wedding. Why would you do that?
I think she's really weak about exercise.
Does your wedding include a marathon? It's hard to imagine not exercising as a valid reason for exclusion.
I just don't want anyone out of shape at my wedding.
Excluding her from your wedding because she's out of shape is really awful. If she's your friend then she should be at your wedding, so I really think you should invite her.