No one here can tell you what a check-in agent will or will not do on a given day and under a given set of circumstances.

What you have not said though is just what the airline said when you talked to them. Did they in fact state that they would not board her even if she has all the documentation you have mentioned?

If they told you that, any opinion anyone here offers you is a waste of time.

You need to clarify EXACTLY what the airline said to you. They are the ONLY authority on a question of what they will or will not do.

If they told you 'forget it, she won't be boarded' then you need to try and escalate the issue with the AIRLINE. Not ask people here if they THINK the airline will relent at check-in.