When N. "Miranda" was first introduced, it was sold as N. maxima "Miranda".
The actual parents are unknown, but Vic Brown writes: "N. Nepenthes "Miranda" is thought by most growers to be Nepenthes x mixta X N. maxima. Note N. x mixta = N. northiana x N. maxima.
There are some other growers, who think this plant is a pure N. x mixta, possibly var. superba.