Give her the opportunity to get ahold of a weapon and kill herself so the drow can't corrupt her - if she thinks it's hopeless, she'd be saving the world from a very dangerous fallen paladin. Better yet, let her do it during a drow ceremony or something, so the people responsible have the wrath of their bitchy god visited upon them or something. Take that, spider-skanks! In return for her noble sacrifice, have her god send her back with no/reduced resurrection penalties.
This would be my favourite option because it's outrageously ballsy, and that's the kind of heroic moment a paladin should get in D&D (or else, see Zeke's thoughts - I think he's very right).
You could also have the drow procrastinate long enough for her to escape any serious physical/sexual torture. Drow are notorious for being slutty and sadistic, but also for petty infighting. Maybe - because a paladin is such a prize, and will undoubtedly bring respect (jealousy) from other drow and favour from Llolth - two or more uppity matrons are bickering over her, perhaps even coming to violence about it. Maybe one of the group who captured her will try to steal the paladin, for her own glory, mistakenly thinking she can handle the pally on her own.
Also, you said they were slavers. Maybe a customer already wants the paladin, and they want her not-disfigured. And (to invoke a nasty-as-hell cliche) if she's the chaste sort of paladin, maybe they want her "pure", so to speak. Waiting for the buyer gives her time to plan an escape or have the other PCs come to her rescue. Make it clear that the drow want to do all kinds of horrible things to her, of course, but an outside factor is making them hold back.