I googles that Burgess gerbil Granola the other day and wasn`t impressed by it so look elsewhere!
It`s good that she enjoys the hay as that provides good fibre and nesting combined. Supermarkets like Lidl/Aldi and the others sell small bags of selected nuts like hazelnuts, walnuts, cashew etc...so check those out. I think gerbils can have pine nuts too. x