Amber wanted to keep coaching and wanted a new deal, so by them not offering a new deal to her that isn't much different than firing her.
Plus BYU doesn't even make contract details public, so we are left to guess whether her contract wasn't renewed or whether she was let go with time left on her contract.
On cougarboard we had heard that her original contract was 3 years due to leaks from somewhere, I presume from the AD.
Even when there is an actual firing, BYU wouldn't announce it is as such.