Is a woman considered an adulteress in the sight of Islamic law if she allowed her ex-husband to approach her private parts after her waiting period, knowing that he did not fully penetrate?

The divorced woman is a stranger to her ex-husband after her 'iddah (waiting period) expires. Therefore, she cannot be treated as a wife except through a new contract. The touching mentioned in the question is not considered zina (fornication/adultery) that necessitates the prescribed punishment (hadd), as the zina that necessitates the hadd is the insertion of the glans. However, it is a sin that requires repentance. Good deeds erase bad deeds, and this expiation includes minor sins through righteous acts.