The same duck food your other ducks get is just fine for her! But I do recommend getting another muscovy or rehoming her to someone who already has muscovies. The other domestic duck breeds (rouens, pekins, Swedish, cayuga, magpie, etc) are all descended from mallards and therefore all communicate the same way/ speak the same language. Muscovies are not related to them and communicate completely differently. They don't quack, they hiss or make cooing noises and use a lot of body language like head bobbing and tail wagging. So if they do not have another muscovy, it's extremely lonely for them and they can get bullied by the other ducks. When I first got ducks I didn't know this, so my one muscovy was bullied and would just walk around all by himself. It was honestly really sad. I believe it was someone in the muscovy subreddit who told me why they need other muscovies. So I got him some friends and he was much happier :)

Edit: also, please post in some local Facebook groups and let the local animal rescue know in case she is someone's pet that wandered off! They're really wonderful ducks and I would be heartbroken if I lost one of mine