How good of a roleplayer is she?
Here is a way to keep her "on the reservation" while building a drow plot for her.
Hit her with a memory wipe.
Hell, hit her with a high level warlock/wizard with a sense of humor who baleful polymorphs her into a Human/halfling/standard elf, and have her fail both saves so she forgets what race she is as well as her memory. (it's supposed to turn you into a rabbit or something and if you fail the second save you for get that you aren't).
Reroll physical stats.
Conserve her hit dice, but convert them to d3 commoner hit dice.
Conserve her physical skill points (Jump)
Delete her trained skill points.
Delete her weapons and armor proficiency.
Give her proficiency in the first simple weapon that she happens to pick up.
She is a *other race* commoner with no memory who speaks only common.
Her alignment aura has been scrambled.
Have her fall in with a retired druid who can tell that her memory loss is magical and that she is either good or true neutral with good tendencies.
He can check with some friends.....
His old buddies, the retired paladin, and the retired CG warlock arrive, they rap, they happen to know of some magic item (inserted into the adventure path X that you want to run) that may be able to restore her memory. They are too old to go with her, but they can train her to be a Paladin/(LG)cleric, a Druid/spirit shaman, or a Warlock/(wu Jen, wizard, psion, wilder...), give her some old magic items they don't need anymore, and she can go get it herself. She just has to choose an alignment. (if she is a really good roleplayer she'll go for the pally or druid)
If she spends skill points on a skill she happened to have previously (other than knowledge) then give her back ranks in it. After she trains with her mentor, give her her old feats back.
Now the payoff.
While you are running Adventure X, throw tidbits into the background that would be relevant to her old life, information that the player will be chomping at the bit to jump on but can't until she gets her character's memory back. You can even have her overhear conversations in Drow. You don't even have to decide what information she over hears, as the pc doesn't remember Drow. Later, after you have had time to think up something, she gets her memory back and then BAM:
1, All the information is made available and relavent to her.
2, She immediately reverts to her old alignment, possibly losing powers (palidin, durid, cleric, and favored soul....why have you been worshipping strange Gods?)
3, all of here old class levels, skill ranks, and features comeback (except see above).
She now has some choices to make:
1, What, if any, priority to give to tracking down that SOB who polymorphed her?
2, Keep the new body or try to get the old one back? (Give up darkvision or sunbathing?)
3, Keep on the Adventure X path or act on Drow subplot information?
4, Keep her old alignment, convert to the new one, or end up somewhere in between?
5, Skip the atoning and just kick a 'lil, or atone...?
5a, Atone to Eilistraee and go on a quest to prove loyalty and convert the Cleric Levels to her service and lose the paladin powers(or if you are gonna let her weasel out of it...convert the Paladin levels to Paladin of Freedom).
5b, Atone to Eilistraee and go on a quest to prove loyalty and convert the Spirit Shaman levels to her service (or compatible underdark spirts, or get her totem animal to go along with the new program...what ever) and lose the druid powers.
5c, Atone to LG God and go on a quest to prove loyalty and convert the Favored Soul Levels to His service and regain the paladin powers.
5d, Atone to the Druids/spirits and go on a quest to prove loyalty and convert the Favored Soul Levels to their service.
5e, Screw it, I'm leveling up in Bard now.
Anyway, this way you can temporally drop her power level (commoner levels), keep her on the reservation while buying time to build a new reservation, and give her some plot hooks and hard choices. What more could a good roleplayer want?