In earlier episodes of Criminal Minds why did Ellie call Gideon DAD a couple times?

Ellie never called Gideon "Dad" in the earlier episodes of Criminal Minds. She called him "Gideon" or "Sir".

There is a possibility you are thinking of a different show or mixing up some details.

It's important to remember that it's easy to misremember details, especially with long-running shows with many characters. If you're unsure, you can always rewatch the episodes you're thinking of or check online resources for more information.