Reddit reviews Essential Idioms in English: Phrasal Verbs and Collocations

I agree with the previous posters; talk with her (in simple sentences until you can figure out her level) and find out about her interests. Using her interests for discussion/activities will help break the ice and make the time more interesting. It may be helpful to have several kinds of activities since your lessons will be so long; a "warmup" game or free talk in the beginning, short reading activity with questions, phonics practice for letters she has problems with, showing her some common idioms and asking her what she thinks they mean (and then explaining), doing a mock-interview to help her practice answering questions, etc. Collocations are something that my Japanese students have problems with because their textbooks don't usually teach them which words sound natural together. You could even buy a book about idioms or collocations if you are so inclined-- this book looks good (http://www.amazon.com/Essential-Idioms-English-Phrasal-Collocations/dp/0131411764/ref=sr_1_5?ie=UTF8&qid=1311644804&sr=8-5).
I am using a different book
(http://www.amazon.com/Essential-Idioms-English-Phrasal-Collocations/dp/0131411764/ref=sr_1_5?ie=UTF8&qid=1311644804&sr=8-5)
with my adult class and I choose which lessons to cover based on their interests. It's rather high-level, though.

Good luck, and don't worry too much. Even if you just chat for the entire two hours, you're giving the girl the chance to actually use and further develop her English skills. If she walks away with more confidence speaking English, it's a win.