Is it permissible to visit a neighbor and accept her invitation after the deceased mother swore that her daughter would not go to the neighbor's house during her lifetime or after her death?

You are not obligated to carry out your mother's will to stop visiting the neighbor. This is because abandoning mutual visits between you contradicts the Shari'ah concerning showing kindness and affection to neighbors. Scholars have explicitly stated that executing a will that involves something disliked (makrooh) is itself disliked. Therefore, if parents bequeath something, it should be carried out if it is permissible according to the Shari'ah, but not if it contradicts Islamic law.