After watching her testimony, I don’t believe she’s even a witness. She didn’t witness anything. I have no idea why they even called her up there.
I believe what the committee chair is trying to do is build a complete picture of everything that went on during that time period related to the issue. Despite how the media presents it, not every witness is going to present some earth shattering and incriminating revelation.
The question is (I think), why did Trump fire her? Was it because she wasn't producing what Trump wanted, which was dirt on Biden and his son and having Volodymyr Zelensky go public with it? Did it have anything to do with pushing her aside and bringing in his own people, such as Giuliani and Sondland?
There may or may not be some ah ha moment in committee's arsenal. But if enough witnesses say the same thing even if it is hearsay, it makes Trump look pretty bad. Here's another thought, since Trump has difficulty controlling what he says and tweets they could be baiting him. In which case, it is working.
Lastly, this is not a trial, it is an inquiry meant to deteremine if the house wants to impeach Trump. The trial comes after that's happened and it goes to the Senate. There is probably a long road ahead before anything is decided....just my guess.