Flight aware shows a 7:53am arrival, so it's possible they will make it. I took that same flight a couple years ago and immigration was right after exiting the plane (so I don't think we were mixed in with other arriving flights) and was very fast. It's a small airport so they'll get to their next flight quickly.
If not, AB is responsible for getting them to FCO. I'm sure they can route them through DUS without too much of a delay. You might look at some alternative routes and send to her so she knows what's possible when speaking with an agent. I hope they get there without too much trouble and enjoy their honeymoon!