homeschool,
I'm with Chalam on this one. I think that you would get bogged down reading cover to cover. Some of the information regarding the divided kingdom (1&2 Chron, 1&2 Kings) repeat the historical information but from different prespectives (Israel/Judah). This makes it confusing to the reader who is not up on this and or does not have an appreciation for how God is working in the Nation of Israel. This is not intended to be an insult in any way. I do recommend reading the Bible cover to cover but breaking it up some New Testament here, some Old Testament there.
I read the Bible cover to cover last year and intend to do it again. It is though difficult to keep going unless you love God's word, which I do. I also agree with Chalam on using an alternative translation. Reading the Bible is a huge commitment of time and the NWT is so biased in favor of WT theology. There are so many good translations of the Bible in English and I'm sure you could use differences in the NWT and others to stimulate conversation with your sister that might cause her to question the motives of the WT and the NWT. Chalam makes some good recommendations of translations, another good one is the New Living Translation. But I would go with the NIV personally.
Take care,
Tom