Has anyone else tried without you there? Can you and DH do a practice for the wedding - go somewhere close, local, just for a coffee/drink to see how your parents go?

She might be fine if she knows you are not there - talk to her about it, tell her mummy will be back after she's gone to sleep and will tuck her in and kiss her good night then. Or something?

At least you'll have some idea of whether or not they'll be ok for the wedding.