Yiwu is generally safe for solo female travelers. There's a low rate of violent crime, but occasional petty thefts, like pickpocketing, can be an issue, particularly in crowded areas. Local people are usually friendly towards foreigners and there are quite a lot of police officers present in the city. As always, exercise general travel safety precautions such as being aware of your belongings, avoiding isolated areas at night and not displaying excessive valuables.