Hmm, they really don't appear to go together. 5 and 6 are very large scale prints and don't really seem to go with the others but would make a very nice quilt as focus fabric on their own with some solids in orange, lime green, yellow and that deep purple. I'm not sure they would work at all with the others in any way.
The fabric your niece designed seems to go with #7 and maybe #4 but not so sure 7 and 4 play nicely together. It is hard to tell without being able to put the fabrics next to one another.
I am thinking you need some sort of solid to unify them. Black maybe?? Rather than making a quilt, you may be better off making a couple of sets of placemats and a table runner with the fabrics that play nicest together and keep the others for your stash.