Personally I would go with the 12 sessions. Assuming that is one a week that gets you three months. A whole lot can change in that time. I would be very up front with her about the abandonment issues. I would also ask about if you use your 12 and have to stop what is the policy about when you can start again. Do you just have to go back to the beginner no of a waiting list, do you have to wait until the demand subsides? It is an understandable but I’ll thought out policy IMO.