Currently row headers require their own property rowHeaderWidth to change their widths. They also work independently from the other columns in such a way that manualColumnResize does not apply to row headers.
It would be cool if row header widths could be resized like other columns when manualColumnResize is enabled.
As a current work around I have added the row labels to my data array, set fixedColumnsLeft = 1 along with readOnly: true and a custom renderer to match the default label styles.
I’m surprised row labels aren’t implemented in this way to begin with.