Testimony can always be challenged. But, the reason for the challenge will determine whether it is sustained or overruled.
If you're saying that the testimony can be challenged because it's hearsay, then I defy you to provide an authoritative cite that supports your assertion, i.e.: someone on the phone cannot testify about what the other party on the phone said to them.
I"d think any challenges would occur where what she says was happening differs from what the 911 calls tell us was happening ~ time line sort of things.
She had nothing to say about the shooting.
I"m with the local cops on this one ~