You’re leaving of a crucial part of that sentence: “…during an internal investigation”

With that, and “work phone” (presumably) implying the phone is Apple’s, she may have given Apple a reason to fire her, even if she deleted the app not to hide that she leaked info, but for other reasons.

But of course, that all depends on what exactly happened. Did she know Apple was investigating, did they tell her to hand in here phone for that investigation, etc.