This is to demonstrate how certain characters would fare against others from their universe.
Higher level characters she could defeat
Gold is more valuable than silver, but is it more powerful? As a matter of fact, in this instance, it is. Nicci's golden exterior does not react as Silverlance's skin does in the presence of excessive temperature. Avatar Prime made sure that no harm would come to Nicci, and that is why he made her impervious to all. Nicci's fighting skills are excellent, and she is relentless. She would hold her own against Silverlance. Only his strength could be a factor, but Nicci's fusion blast would be an asset in this fight. Its excessive heat would make Silverlance's skin turn red, increasing his resistance to temperature but lowering his resistance to physical attacks.
When the two did fight in the past, the victory was Caregiver's. She was stronger and with the use of her life drain, almost managed to extract Nicci's soul, which would have caused her death if not for the intervention of Avatar Prime. Today, however, Nicci's power has increased. Her strength has remained the same, but she can now fly and discharge energy blasts which would easily counteract Caregiver's florakinesis. Caregiver's only advantage is her strength and life drain, but Nicci's fighting skills surpass hers and her sword would keep Caregiver at bay. Caregiver could still potentially win if Nicci was careless.
Sadly, Warbot would stand little chance against Nicci, mainly for the fact that Nicci is faster, and her sword would cut through his armour. Each could repel the other's energy blast, so fighting in this fashion would prove useless. Warbot only has strength on his side, but it would not do much against her indestructible golden skin.
Lower level or same class characters she could NOT defeat
Nicci could never defeat Renshi in battle, and her energy attacks would be useless against him. Nicci's sword is one of the most powerful weapons known, as it has been shown that it can cut a guardian, but whether it can cut Renshi is in doubt. Renshi's skin seems to be as invulnerable as Nicci's golden exterior or Silverlance's silver one.
Her only way to survive this fight is for her to fly away because Renshi cannot fly.
Arkahnus cannot be underestimated, and Nicci would need to be careful against him. Arkahnus cannot only create force-fields, but he can manipulate them as well. Arkahnus has killed many Gatari in this fashion. He has used his force-fields to crush enemies or make them explode by inserting them in their mouth. Arkahnus is quick and can teleport faster than Nicci can move. He is not as skilled a fighter as she is, but he can fight her from far.
If the two fought, Nicci would be at a disadvantage unless she struck quickly. Nicci is faster, stronger and powerful, but Spell Weaver's magical arsenal could defend against all of these and Spell Weaver has the means to entrap her and restrain her. Whether she could actually kill her is still in question.