Is this a GDPR breach

[i.dan]

In a private email I provided a screenshot of my financial information to my ex-partner for the purpose of showing that I had the funds to buy out her share in a property.
At the time, she was still a Director of a Company of which I was a Shareholder.
At some point either while she was still a Director, or after retiring from being a Director. She disclosed this information to the Company.
At that time I was taking the company to court over a claim for a breach of contract.
Her reasons for sharing the info was that they could use that information against me in terms of claiming costs.
Question is.
Is this a deliberate breach of GDPR rules?
or, is does it depend on whether she shared that private information whilst being a Director?
Are there rules that state a retired Director must respect such rules even after retirement?

And, if it is a breach.. what possible penalties are there for stress caused by such a thing?

[atticus]

You might start by checking with the ICO whether your ex is a data controller, i.e. whether data protection laws apply in this situation.