I agree with PoB that the standard DnD setting material leans strongly towards a 'back & white' 'good Vs evil' morality - for the reasons he's already pointed out. In essence, in such a setting, there
is a universal standard of morality - killing innocents is bad, slavery is bad, torture is bad, etc. - & alignment can play a big role in such a setting.
If I recall correctly a god's Clerics can be up to one position away from that god on one of their alighment axis - so a Lawful Good god can have Lawful Good, Neutral Good, & / or Lawful Neutral Clerics in his / her / its employ.
I asked about the slavery thing because in fantasy settings, especially DnD stuff, there are societies with (by modern standards) pretty enlightened morality systems.
Historically pretty much any society you'd care to examine has had slavery in one form or another - & in most cases it wasn't really such a bad thing as fantasy settings suggest: they tend to take their que from the (relatively recent, historically speaking) European / American trade in African slaves - which was far worse than most older 'slavery' systems in many regards. In many historic societies slaves were closer to our more modern concept of a 'wage slave' (i.e. someone who has little choice but to do the job they've ended up being stuck with) - slaves could often earn their own money, gain freedom, rise to any level on the social scale, & often had better living conditions than many poor non-slaves (in fact, in some societies, people would sell
themselves into slavery rather than live the life of poverty). In such a society slavery wouldn't be 'evil' by its very nature (in fact, the original 'utopia' concept was based around a society where a slave class did all the work!) - in DnD (& PoB's setting) it
is evil by its very nature: so it makes perfect sense that his Lawful Good ruled society wouldn't allow such a thing to exist within its borders.
I'll think some more on the ol' back-story... but there's no way I'm having a character enslaved to a
Hobbit (which, by the way, is all copywright & stuff by the estate of the late, great, JRR - so we should probably stick to calling them 'halflings' - & in any case, the halfling pictures in the new DnD books look a lot nicer than any hair-legged ol' Bilbo!

).
I'm thinking that she (my character - as yet nameless 'Barbarian chick') was captured in her homeland by an enemy tribe & traded to the desert nomads for horses (selling captured enemies into slavery being a relatively common occurance in that part of the world), like PoB suggested, ending up in one of the great opulant cities of the region. There she was trained in befitting skills (sandwich making & the like

), before... [insert how character gets hooked up with other PCs]. I'd quite like to steer away from the old 'hated her new life & escaped' bit - since her new life would have been filled with wonders undreamt of in her homeland, not to mention regular meals she didn't have to kill & skin herself, shelter of the most comfortable kind, nice new clothes, & all those other comforts & luxuries which come with so-called 'civilisation'. I'm not planning on playing her as totally subservient or anything (not with that firey feral Barbarian temper just under the skin), but just as 'relatively content with her lot in life'.
I guess if their are no appropriate PCs (halfling rangers
not being noted for their slave-ownership, for example

) having her along with one of the NPC merchants would seem to make some sort of sense. Of course if you, PoB, are uncomfortable with the idea of an enslaved PC then I can dream up some way she's obtained freedom - maybe her master fell for her & freed her to marry her or something? I just thought it'd be an interesting concept to play.
<span style='font-size:8pt;line-height:100%'>"<span style='color:green'>To be honest, agent Falcon, I am quite insane. As for my plans, vell, I plan on transforming ze two of you into obedient zombie übermensh. Zen, I plan on, very inappropriately, touching your fraulein friend about ze chest and backside. Shall ve begin</span>?!"<br />Doktor Kharnov von Kripplor, Danger Girl<br /><br />"<span style='color:blue'>I'm invisible. It's a confounded nuisance, but I am. That's no reason why I should be poked to pieces by every stupid bumpkin in Iping, is it</span>?"<br />Griffin, The Invisible Man</span>