Your MIL likely loves you, stutter and all. So while you should certainly be as relaxed as possible, I don't think the stutter will make your MIL angry if she hears it in that tape. I like the idea others had of having it prerecorded, then at the garden, simply hit 'play,' and then hold up visuals. Photos of places, events, people. Then you won't be so nervous. Get your DH to join you or even your MIL. Dance while you're being taped maybe, while your 'lines' are being recited? If you don't want to speak at all, team up with the DH as the others have said.