Interesting one.
https://www.bbc.co.uk/news/uk-66648763
I presume Sandbach is thinking of something related to the 'right to be forgotten' but I can't see how it applies or how it could be extended to apply.
https://ico.org.uk/for-organisations/uk-gdpr-guidance-and-resources/individual-rights/individual-rights/right-to-erasure/
The link to Al Nasir's search for his 'roots' in the article is fascinating.
https://www.bbc.co.uk/news/extra/3k9u8lh178/Searching_for_my_slave_roots
An interesting one this.
Surely if this is simply a statement of fact how, or why, would it not be reasonable to make that point.
However I guess the issue is about inference beyond the factual. In other words is Sandbach guilty by associated. Now in its broadest sense, well of course she isn't - she cannot be held responsible for the actions of someone many generations previously, regardless of whether they are related. So while it may be factually accurate it becomes irrelevant.
But moving on further, I guess a case can be made that Sandbach may have benefitted from advantage that accrued from the actions of her relative. In this case it does become relevant, but would need to be based on a pretty clear evidential trail. So simply making an argument 'Great, Great Grandaddy was super rich because of slavery and therefore so are you' seems too vague. You'd need to have some pretty clear trail of inheritance of wealth and/or influence. In this case, there does seem to be a strong link in property terms between the proceeds from slavery and ongoing business arrangements that Sandbach is involved in now and benefits from.
Now this might be sufficient to conclude that the information is in the public interest (I think it probably is) but that is a different matter than implying that Sandbach somehow owes reparations although I'm not sure this is being suggested anyhow.