Story-wise... if the child is a bastard between this Warlock and a halfork prisoner... that probably means the babe was raised by the Warlock (or at least by someone in the Warlock's circle). She seems powerful and willful enough that *if* she took liberties with prisoners, and *if* she got empregnated by them and actually took the baby to term... she wouldn't just dump it altogether. She'd keep the bastard somewhere within her sphere of influence. Maybe she doesn't raise the baby directly, but she also doesn't let it leave her auspices. If she wanted it enough to go through the entire birth process, I don't see her dumping it at the first opportunity.
So this means that this bastard child has been raised under the auspices of a drow/high elf Warlock, so I would imagine it grew up surrounded by more elvish influences and learning than any human or orc. So the drow/elvish half of the quarter-breed would have dominance (in personality at the very least). The babe would probably be bigger and slighter stronger than your typical drow or elf due to its human/orc side... but that might only show up superficially in other ways. Skin perhaps a bit ruddier, ears slightly rounder, more impatient and quicker to anger than a normal longer-living drow or elf. But for the most part... the character comes off more drow/elvish than anything.
Mechanics-wise... you probably can start with the basic high elf and then tweak it slightly to indicate its drow, human, and orc influences. Perhaps prefer crossbows over longbows. Give a -1 to Charisma and a +1 to Con on top of the normal high elf racial bonuses. Stick with low-light vision (or the campaign equivalent.) Other than that... the character is such a mixed breed that you probably are best off just using one primary set of racial traits and subsume the other races into the personality and story, rather than the mechanics. You don't want it to mechanically become too much of a ridiculous mish-mash.
