Meet somewhere for the introduction and do a kind of placement test to find out her level and problems. Don't charge for that lesson, just get to know her. It can be done in a cafe, that's how I always meet my potential students. If after the meeting we decide not to meet again for some reason, it's also not a problem.
During the meeting, ask what kind of an interview is that, what is she supposed to speak in English about. I hope she knows something about the structure of that interview. Is it only work-related issues or they want her to speak about her freetime activities as well?
Next, insist on an intensive course. 3 1 hour lessons is not enough unless you can pour English into her mind with a jug :-) Every second day for 1,5 h is good. People always say they want to brush up but then you find out that they cannot relate DOES to the third person singular question!
Peter Easton gave good tips. Try asking different questions that need answering in different tenses, using gerund, conditional sentences; ask her to translate something to see how prepositions work.