On its own, Mage Armor is a lackluster power. However, if you combine Mage Armor and Fire Shields, then BOTH powers become more useful. Without Mage Armor, monsters can deplete Fire Shields quickly -- because monsters can hit Asharra more often, and every hit consumes one of her four Fire Shields. On the other hand: with Mage Armor, Fire Shields can last longer; monsters would have to bypass her Mage Armor first before hitting/consuming her Fire Shields.

I generally select Mage Armor + Haste as Asharra's utility powers. Both Mage Armor (utility) and Fire Shield (Daily) are free actions, so I always activate both defensive powers during Asharra's first turn. I replace Mage Armor with Web only for certain bosses and quests. For example: I used Web on Ras Nsi, so the boss could not move in and melee my heroes.

Fire Shield retaliates more than one damage after you upgrade Asharra's secondary weapon. It can deal up to six damages with upgrades.

Likewise, Mage Armor also provides up to +6 bonus to Armor Class after you upgrade her accessory. +6 is a hefty bonus to AC.

Chromatic Orb has a longer range (one more tile) than Acid Splash, so it has its uses. (Acid Splash is within one tile; Chromatic Orb is within two tiles.) I generally combine attacks with different ranges to deal with different situations. There were situations in which I used Asharra to attack a monster that was more than a tile away.