Is what the questioner did—uttering the words “Ah, ah” to her deceased sister’s husband with the intention of helping him expel accumulated semen from his body—truly something for which she will be held accountable religiously and that will affect her fate in the afterlife?

There is no religiously permissible outlet for lust other than one's wife. It is not permissible for a man to seek sexual practices outside the framework of marriage, nor is it permissible for a woman to respond to such a request. One must repent to Allah and firmly resolve not to return to such acts, for Allah accepts the repentance of those who repent. The woman should increase her prayers for forgiveness (Istighfar), conceal herself, and not inform anyone of what happened. As for the man, he should treat himself by marrying or by fasting.