I agree with what PP have said above. DD8 has that lexile as part of her range. At that level, your DD absolutely needs more challenge than the typical 3rd grade reading curriculum will provide. Does your DD's school have G&T reading or some sort of differentiation/acceleration?

In the meantime, keep her reading. Let her read in, over, and even under her lexile - you are right in thinking that a love of reading is key.