Hmmm .... remember this woman has not invited this information and that being too aggressive may throw her defences up.
If you were to write her a short letter, thanking her for her offer, but stating that you no longer wish a bible study with the Jehovahs Witnesses, then proceed to give her a short bulleted list of your reasons i.e. NGO of the UN, child abuse, 1914 chronology etc. Say you have come to this conclusion having researched the Jehovahs Witnesses since requesting the study, and give references to appropriate sites i.e. http://www.un.org/dpi/ngosection/watchtower.pdf & www.silentlambs.org .
You may wish to append a copy of the letter from the link above, and maybe some information from silentlambs, but keep the first page simple just to sow the seed. If you are going to include the appendices, you should tell her on the first page (albeit at the bottom), so that she doessn't feel you have trapped her into reading it.
She will read it as she will no doubt be intrigued, and she will probably feel her faith is such that she could not be phased by anything she reads, but by the end of it she will have serious doubts. Now, depending on how hard she suppresses it, a couple of years later with any luck, she will be writing her own letter to all of her misguided friends.
Groovycat