I believe Necromancer is one of the great unfulfilled aspects of 4e, personally. It is such a powerful archetype it really deserved its own class, with its own builds beneath it. I think unique companion and horde mechanics could have been implemented, but around Heroes of Shadow the design philosophy really seemed to shift. The Shadow power source in general was kind of shafted, and deserved its own treatment, not any sort of odd piggyback on others. Just a real lost opportunity there.
That said, we've been able to get a lot of traction out of hybrids and multiclassing in my groups, and, most of all, reflavoring. I think you took the right approach, cherrypicking powers you felt spoke Necromancer to you. I think every race offers something special when combined with the idea of necromancer, and sand-form genasi sounds particularly sweet. Did you have any notions, or did you friend's gf, on how the character was going to be played? Does he shift into sand and exhume choice bodies? Or does he bury his victims alive? I think that also has something to do with being a Necromancer, the approach to the character in the game itself. If a character takes on the air of a necromancer, and the other PCs kind of recognize it, it goes a long way to empowering them and thus creating a fulfilling necromantic experience (even the character is really a mage or, hell, bard). The DM can also go a loooong way in making her feel more Necromancer in certain effects descriptions and plot ties (induction into necromantic orders, rivals and enemies of the Raven Queen faction, etc). It's a group effort, but it's completely possible.