Lying is a much more common behavior among people - adults as
well as children - than we like to admit. We have several
phrases like - 'stretching the truth', 'white lies', 'fibbing',
'bending the truth' all of which are euphemisms for lying. "The
traffic was terrible" is a common lie that many adults use to
explain why they're late to work - though the traffic is often
indeed terrible it's usually not the reason we're late but we
lie and say it is.
So that a 5th grade girl would lie isn't out of keeping with
the culture of which she's a part. Goodness, we find lying at
the highest levels of society including Presidents of
corporations and Presidents of countries - so we have to
understand why a child might think that lying is commonly done
and even an acceptable response.
The question is - on what occasions does she lie? Is there some
common and repetitive problem that she lies to contend with?
To consider her lying, it would be essential to know in what
circumstance(s) she's lying. Her mother is ill and she fantasy
lies that her mother is well? She's late to school because
aliens abducted her? The dog ate her homework?