You might see if your vet can get you a sample of the Oxbow Regal Rat, before you buy a bag. My rats HATE the Oxbow. And to be honest, I haven't heard of many rats at all that liked it. This is sad, because it has perfect nutrion content and is very good for them. But mine toss it right of the cage on the floor in protest. Not to mention, it smells funny.
Sounds like your little girl is still fear pooping. But you may want to consider having your vet do a fecal test to see if she might be carrying any parasites. Antibiotics can help clear that right up.
I am not aware of anything a rat or rabbit can carry that would not be species specific. Therefore, I would not be concerned about QT unless you have other rats. Your ratties would not carry anything that could be passed along to a rabbit. Even mites/lice are species specific.
Rats are very much like us....when presented with yummy options, we might tend to eat that before the "good for you" stuff. But if you already have skinny ratties, I would be more concerned about getting some good weight on them too. Another good suppliment is Nutrical. It comes in a tube and can be mixed into babyfood.
I tend to have the opposite problem....my ratties are little fatties
. Every night for dinner, they get a starch (cooked pasta, rice or sweet potato) several veggies (examples: peas, corn, broccoli, cooked green beans, canned cooked black or kidney beans, kale, cilantro) and a fruit (blueberries, banana, grapes, melon). We also give them soy yogurt, oatmilk or soy milk.
My husband tells people our animals eat better than he does....it's true! lol