She shouldn't have any issues unless she decides to quit on you. Muscovies have a much longer incubation period than chicken eggs (35 days if I recall correctly which is two weeks longer than chickens). There's a possibility that might be a bit long for her. I would just have a backup incubation method to be on the safe side.
Also, if she has hatched chicks before, she may realize they aren't chicks and reject them. I attempted to get my broody hen to adopt a couple ducklings and she was not happy about it. You would think I put turtles under her or something the way she reacted. She had adopted chicks in the past and I ended up having to go find her chicks last minute this time, which she took without hesitation. Might be different if they actually hatched under her though...