La Union in El Salvador is somewhat safe for solo female travelers. Like any other destination, it has parts that are less safe than others. The local community is generally friendly and helpful, but it's always important to be cautious. Avoid isolated areas, especially during the night, and be aware of your belongings at all times as petty crime can occur. Local law enforcement is somewhat reliable, but it's recommended to stick to tourist-friendly areas as much as possible. If you follow basic safety precautions, your trip can be a rewarding experience.