There seems to be at least one other Jordis around, an American musician named Jordis Unga. This may be where your grandchild's parents found the name.
I suspect that it's an altered form of Jordan, perhaps designed to make a feminine name out of the masculine Jordan. It also reminds me of Jadis, which is the name of the White Witch in C.S. Lewis' "Narnia" books. Jordis may be an alteration of Jordan which is meant to sound like Jadis, an alteration of Jade.
♦ Chrisell ♦
All we have to decide is what to do with the time that is given us. - J.R.R. Tolkien.