The oath is quite specific indeed and tricky. But she can do non-lethal damage to spiders or use her powers to try control them or disable them harmlesly. But she cannot anyway command her followers to kill them, encourage kill the spiders nor use any effects which has potential to cause great harm to spiders (or instant death).<br/><br/>Any failure in this regard breaks her oath and turn our matron mother into a drider as sign of Lolth's displeasure (and looses this feat until attonement done by higher level cleric is done on her and that does not remove drider condittion).