Niquita Maldenado is mostly a mystery. Apparently, Melvin Frohike was her partner in the dance of Tango. Frohike was a legend known as "El Lobo" and it is likely that Niquita was his partner for years. Given how angrily she reacted when he appeared at her workplace, it can be inferred she was more than just a dance partner. Despite her long tirade, that revealed how Frohike left her, she was nonetheless won over by "El Lobo."
She aided the Lone Gunmen by once again dancing the Tango with Frohike so they could foil the smugglers and intercept the composite.
She kissed Frohike goodbye and they parted on amiable terms as the smugglers were hauled off in handcuffs.(The Lone Gunmen : Tango de los Pistoleros)