I wonder if the best way might be to ignore it, make your own music which sells on its artistic qualities - and we know that Lily Allen can do that - and if you want to make a point, speak about it in interviews, tweets, and so on.
As TimC says, shes' got to make money from the system while dissing it - but dissing the system is part of the system! We don't really have (I think) a "counter culture" nowadays, everything's more or less mainstream. Well, Allen is certainly mainstream. But at least she's trying.