It depends on where you want to push things to: If you want her just to stop believing in the WTS, you can choose scriptures that contradict the Borg's regulations and practices -the jwfacts.com site is the reference site with regards to this.
However, if you want her to go one step further and become an atheist, start from scratch. Start with the Genesis account of creation: Notice the 2 different stories of creation that are presented in chapters 1 and 2. Read about the preposterous ideas of seperate creation of animal kinds: e.g. why on earth would God create the whales family as mammals and put them in so much trouble living under the water? Continue with the hilarious account of Noah's flood, note that God said 'all' living things would be destroyed: what happened to the fish?
Then go on to the Bible's main theme. What is that? Love? God's Kingdon? Er, no: it is KILLING. Murder, manslaughter, execution, you name it. See all the transgressions of the Law that brought the death penalty. See God killing in an instant poor guys just because they happen to do something bad, such as giving 'inappropriate' offering of sacrifice. See the complete slaughter of all the first-borns of Egypt, just to 'give a lesson' to bad Pharaoh. See the Levites slaughtering their fellow nationals because they made an idol. See God giving food to Israelites and then killing them just after they ate the food!
Then continue with the UBER-Genocide account of Joshua and Judges, starting with the annihilation of poor Jericho: See how Jehovah instructed the Isrealites to slaughter EVERY human being (and livestock!) of Canaan, men, women, INFANTS, just because they happened to be born Canaanites. Read the exact instructions, read carefully the whole chronicle as an outside observer, and feel your stomach get sick.
See how God rejected Saul; why? Beacause he was a murderer? No! Because he was not murdering enough! He hesitated to slaghter the Amalekite king, and so the pious God-fearing Samuel (yes, that sweet Samuel who served in the temple from infancy) cut the king's head with a huge sword. See then king David cut of the foresking of 100 Philistine penises and bringing it as a bridal price. See God killing 70.000 Israelites beacause of a mistake tha David made! (which was the terrible sin of census taking). See Solomon becoming known as a king of Peace, only after he had all of his potential rivals slaughtered.
Read the account of sweet Esther. See how Jews in the Persian empire came close to suffering a genocide by the 'bad' Aman, but then see how triumphantly THEY killed every one (and their families) whom they considered an 'enemy' for their nation.
The list is endless. Plenty of material for ''Bible study"...