That’s the age we got Willow at. Same here, first time I had a baby and didn’t realize she was really too young. All went well here though.
We fed alfalfa hay, mixed with orchard and timothy, and alfalfa pellets. If you don’t know what kind she was fed, I’d recommend feeding a few pellets at a time and make sure it doesn’t cause any stomach upset. We use a bowl for water. It’s one of those that attach to the pen, so it c an’t be spilled. If your’s is anything like Willow, they are little poop machines, so it should be quickly noticeable if anything is going wrong. Since their digestive tract is still maturing I would go to the vets if she stops eating/pooping for any length of time. (I think I’d of been full panic at the 12 hour mark) The poops should be little compacted dark balls. (the alfalfa makes them dark brown, instead of a lighter brown)
At twelve weeks is when it’s recommended to start adding greens slowly. Add a little of one and wait at least 3 days before adding another. Jot down notes if you will have issues remembering which ones you’ve tried.