Is it permissible to travel to visit one's mother, who lives approximately 68 kilometers away, given that there is a disagreement with the husband about this trip, and that the questioner shortens and combines prayers during the visit?

The travel that is forbidden for a woman is whatever is considered travel, whether long or short. The husband should assist his wife in visiting her mother, as Allah Almighty says: "And cooperate in righteousness and piety." If it is not possible for the husband to travel with her, or for a mahram to accompany her, then permission can be sought for her to travel with trustworthy companions, as some scholars have permitted this. If travel is impossible, then she should maintain ties with her mother through available means, increase in supplication, and try to persuade her husband.