What exactly is the role of an LVN in an ALF?

Depends...first and foremost I'd advise you to research the BON on ALFs and what should be going on in one. I have LPN friends in ALFs in Florida, (I'm guessing you are in TX, or CA since you said "LVN") and they pretty much supervise med techs, and make sure Rx are updated, and etc.
Ask if you'll be the only licensed one there, don't hesistate to ask exactly what it is they want you to do. How will training be? Will you pass meds or techs? If techs are passing meds, what limits do they have? Who is your resource person? I'm sure once you find out exactly what the job entails, the questions will come naturally, but these were a few that I can think of...Good luck!