Hi Lisa,
If you got Journal Entry without and GL details then I believe it's okay ( I may be wrong) But if it has Distribution details i.e. Save Transaction should not allow to delete.
If you goto -->Tools-->Setup--Financial -->General Ledger--> Check 'Deletion of Saved Transactions'
This will block user to delete already saved Journal Entry.
Let me know how it goes.
Thanks much
sandip jadhav