Under oath doesn't mean jack shit to somebody who is guilty as sin in the first place. I'm sure they could get her for perjury if they wanted, but its really no different than somebody who is testifying in their defense and bullshits their way through their testimony. Its usually just marked up to "we don't believe you." In this case, she pled guilty to the charge in the first place so it really doesn't matter that she made up a bullshit excuse. She pleaded guilty to the theft and just put that out there to have a scapegoat basically. Innocent people do not plead guilty in this day and age.
I don't really know enough about the case. What the charge she pled guilty to?
Hypothetical:
"You're accused of improperly using a company card to make personal purchases for yourself which is regarded as theft and carries a sentence of up to 10 years in prison. How do you plead?"
"Guilty."
"Okay...case closed if you plead guilty to stealing from the company."
"Wait, I used the card, but I was told I could as long as my family member played football at Alabama."
"Yeah, right. If that was true, you shouldn't have pled guilty."
If that's how it went down, then I have no reason to think she wasn't telling the truth. But as I said, I've got no clue how it all went down.