Praise in public, criticize in private
In my (considerable) experience of working in large organisation (private and public), whether this works or not depends strongly on the power differential between praiser/criticiser and praisee/criticisee. Basically this is the most likely outcome: she got it wrong.
Slavery is much older than the period that the term "scientific racism" refers to. Older slave holders had no trouble justifying slavery.
Interestingly, the many slave rebellions of antiquity (and after) by and large did not seek to abolish slavery, only to switch who's a slave, and who's a slave holder.