In terms of the dishes, stainless steel is considered more hygienic than plastic. If the breeder had the dishes on the floor then it could be that the bird hasn't found them yet and a floor dish would be useful or maybe it is perhaps just preferring the 'treats' that you've added in there.
I personally don't cover my birds cage at night BUT they're in a separate room and not disturbed after dark and the temperature doesn't change much overnight.
It's recommended to cover the top & 3 sides of a new birds cage whilst they settle in. If you feel that the bird is settled and choose in the daytime, to push the cover back from the sides so that the cover is just held mainly between the wall and the back side of the cage, then just slowly easing it forwards and down at dusk, should be less dramatic than a big dark cloth suddenly sweeping over the cage in a lit room, if you get what I mean?!
Do you need to purchase anything else? It's a bit difficult to comment without seeing the cage (cuttlebone, mineral block, dish/clip for veggies, natural perches).
If I were you, (I'm not sure what internet access your niece has/is allowed) I think it would be a nice idea to copy & paste & print out a lot of the 'stickies' on this site and put into a file to make a little budgie care/information resource for her to read through. A budgie file to peruse would also be a good diversion, as for most 10 year olds receiving a new pet, I think the most difficult aspect for them is to let the pet have a bit of peace & quiet.
Im sure she'll be delighted!
Maybe see you back soon with your own little budgie.