After i complete her quest..should i slay her for XP and treasure?

Urm... up to you.

Generally, good people let her live, evil people kill her.

Will I lose Rep points for killing her?

I agree with Dundee. If I were in you place I wouldn't kill her.

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Where there are monsters and barbarians there will be Byronas fighting against them.
Leader of Keldorn's Order

It's a question of whether you are interested in role-playing, or powergaming. If you are just in the game to get Xp, then kill her. If you are interested in role-playing and are good aligned, it would be totally against your character to kill her.

Bear in mind that good aligned NPCs may well object if you do kill her.

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Time is an illusion. Lunchtime doubly so.

Epona of The Laughing Hyenas
Proud winner of the 'Most Useless Post 250 Has Ever Seen' Award 2001. "I'd just like to thank my friends and family, without whom none of this would have been possible..."

No, there is no REP loss for killing her, but what she drops (sliver dragon blood) is used to make an item only usable by evil chars, shes worht some nice XP tho, so its up to you.

I've always played good or neutral and have never killed her, but if you are Evil, I'd say go for it.