Is a woman considered an adulteress if she felt pleasure while a man was attempting to penetrate her, but she screamed and stopped him, and she is unsure whether he had penetrated her or not, knowing that she is remorseful and repentant and has promised Allah not to return to such an act, and will her repentance be accepted?

The default is non-penetration when there is doubt about it, for the rule is that certainty is not removed by doubt. What transpired between you two is a form of adultery (zina), which is an outrageous and grave matter, but it does not necessitate the prescribed punishment (hadd) as long as it did not reach the point of penetration. What is obligatory is to repent to Allah and regret that action, and to sever the causes leading to it.