that was true with the old school batteries. The new lithium ones, that has no effect. Stores don't know this b/c companies don't teach them. Sorry!
As far as your battery life: If you have ever had a windows phone you know the deal. However with Droid it's not that bad though. If she set her emails to sync every 5 minutes, yes her battery will drain. If she sets her facebook, twitter, etc to sync often that's the problem. Go and make sure all things aren't constantly syncing.
