You should aim to eliminate Amira as soon as possible so she can't activate her gold.
Amira can be countered by Agility heroes who do not have the critical hit stat.
Another way to counter Amira is to use heroes with high magic defense so even if she activates her gold, your heroes can survive and eliminate her on the next round of attacks.
You could also use heroes that cannot be the target of some of her skills. For example, Amira's "Endurance Test" skill will target heroes below some health threshold (569128 health at maxed-out state), and the "Genie’s Patronage" skill will target heroes below a specific magic damage level (45298.7 at maxed-out state).
Cornelius hits the enemy with the highest intelligence with his "Heavy Wisdom" skill. He also increases the team's magic defense with his "Protective Dome" skill.
Amira's "Genie’s Patronage" skill targets heroes whose magic damage is lower than 45298.7. Xe'Sha (maxed-out) has 78312 magic damage so she stays out of Amira's radar.
On the other hand, Amira's "Endurance Test" skill targets heroes with health lower than 569128. Lilith (maxed out) has 624336 health making her a great exception.
