Not sure about the twitching.
One straightforward way to know she is getting the best food is to get a good quality duck or poultry feed. If you get poultry feed you would be best to add a tablespoon of brewer's yeast once a day to the food. Not baking yeast - brewer's yeast - it is a supplement.
The Stickies are a good source of information, so is Storey's Guide to Raising Ducks.
If you are with her 24/7 she will probably be fine. It is a lifetime commitment. Some people do this.
They get very ill and often die if they eat something metal that does not pass out of their body. If they get into dead plant or animal material that has started to rot, they can get botulism and die. Eating string or rope or fabric can stop up their digestion and that can be fatal. There are several poisons that can kill them, including fertilizer. It's best they not get into onions or garlic (although some people use little bits of garlic sometimes for worms - I don't know much about that myself).
Caffeine is very bad for them. If I drink coffee or tea near them, I don't put the mug where they can get into it - and they do try to get into anything like a mug or a bowl.
