(salary) seemed high so I questioned it
With whom? If it was with other/another member(s) of staff, that may be construed as gross misconduct.
I'm struggling to see your case here, to be honest. If I've read your post correctly, this all played out over the course of less than a week. I can't see how it meets a claim for substantiated bullying, or constructive dismissal.
If I was to guess, and correct me if I'm wrong, you spotted that this woman was on a higher salary than you, felt aggrieved, spoke to others about it, were reprimanded by a director for this, things got heated, you resigned, directors felt you were a liability for your notice period so are paying you in lieu.
Also, you said you were pursuing unfair constructive dismissal. Which one? They're two very different things. For unfair dismissal, the onus is on a company to prove that they did not dismiss somebody outside of fair and natural justice (i.e., policies and procedures clearly set out), or equality/protected disclosure legislation.
In this case, you resigned so I don't think a court will look at unfair dismissal.
For constructive dismissal, the onus is on the employee to demonstrate that there was no other option for them but to resign, typically following a period of harassment, and having exhausted all other channels (company's grievance procedure, mediation etc). Again, I'm struggling to see that here, but accept the timeline may be much longer than I've picked up in your post.
Best of luck, OP. Will you post after the hearing- I work in this area and always interested in case studies.