I would go with United 933 and 5.10pm departure from Frankfurt.
1hr layover in FRA is doable.
You can sleep-in after a good wedding party (and if you are celebrating with italians - you will value every minute of sleep on Sunday) and be back in lovely d.c. in the evening.
My girlfriend and I did this a few times in the past and we will be doing it three times this year (same reason - wedding and need to get home Sunday night).
Our feeder flights won't be Italy, but I never had any issue making this connection.