Bettina Aptheker makes these charges knowing that he cannot defend himself from beyond the grave.
Just because she says it is true, does not mean that it is - no more than any allegations of molestation or rape are true. Of course we cannot exclude the possibility that it did happen. But possibility alone is not reason to destroy his reputation.
His death puts the issue beyond the law. But the morality that lies behind the legal rule, innocent until proved guilty, stands. Things would be otherwise if corroborating evidence were produced - as for example was the case with Fiona MacCarthy's discovery of Eric Gill's journals recording his abuse of his daughters, but until such is produced, it is wrong to endorse the judgement against Aptheker Sr..
Aptheker Sr. was quite wrong on many things - mostly because of his adherence to the political line of the CPUSA, which committed him to grotesque positions on Stalin and Hungary; the social chauvinism that informed the CPUSA's commitment to the US war effort manifested itself in ugly xenophobic slurs against Gunnar Myrdal, for example.
Aptheker disguised the underlying reformism he was committed to in the present with a rhetorical leftism in the history of slavery. Unfortunately that leftism meant that he projected an unrealistic proto-revolutionary consciousness onto slaves that was in truth only very intermittently present. That was why it was Eugene Fox-Genovese who was more often correct than Aptheker in their long-running debates over history of slavery (however unfortunate the later development of Genovese's thinking).
Sadly, any clarification of Aptheker's political errors is dinned into silence by Bettina's miraculously recovered memories, and any value that might be got from her life on the left overwhelmed by this one grotesque allegation. The personal, to state a lesson the CPUSA forgot, is not political.