It's great that Bible studies these days can find out facts about the history and doctrines of JW thanks to Internet. Before you end your study, I suggest you show the lady actual quotes of changed teachings from wt publications. Use jwfacts.com and copy the actual quotes about 1914, 1925, 1975, 'superior authorities', 'this generation', etc and paste them into Word. Then print it out for her, maybe she wouldn't read printouts from an internet 'apostate' site. I know it might take some of your time, but they're just WT publications, so she should not object to reading them.
The reason why I say this is because some time ago (while I was still mentally inside the JW world), a girl I used to visit showed me a book written by an ex-JW. She'd read most of it and told me about the false prophecies and Deut 18: 20-22. I wasn't able to provide her with a satisfactory justification for them. I asked an elder in our hall how I was to answer someone in this kind of situation. He basically told me if someone had read this info, he/she is a lost cause and I shouldn't bother anymore.
Months later, I started doing my own research after finding out about the UN involvement and other issues. But what this person had the courage to show me left an impression on me, and certainly planted doubts in my mind.
If you care about the lady visiting you, please give it a try. You never know what the effects could be. She might thank you later. Or she's stick to the cult.
Also, now that you attended the KH once, you've given her 'hope' about you actually enjoying the meetings and maybe going another time. Tell her you're busy next time, or better simply say you already gave it a chance, but don't feel like attending again.
