Aversion field is Renata's gif tto deflect any and all kinds of physical assault.
It mainly works by making the attacker temporarily forget her or his intentions and motivations and go the other way. Eleazar has mentioned that she can project her shield several meters out from herself to protect those of her priority. The force she uses is almost unnoticeable.
Renata mainly uses it in protection of Aro, and she needs to be physically in contact with him in order to fully protect him with her gift. On occasion, she would include Marcu sand Caius in her shield.
This power is more restricted than Bella Swan's. As, like many abilities, it is psychic, it does not influence Bella or those she protects.
Also, since her power works by repelling an attacker pursuing her, it probably has no effect against a long-range supernatural talent, such as Jane's pain illusion or Benjamin's elemental manipulation.
Renata's gift was manifested by her strong desire to protect her family from pursuers as a human. She stayed with her great uncle Luca to protect their family after her transformation--until the Volturi heard of her talent and offered her a place within the guard. With encouragement from Luca, she agreed and had since become the personal bodyguard of Aro, the leading ancient of the coven. She was emotionally bound to the ancient due to Chelsea's power.
No one has ever been able to come near her or her charges without getting repelled by her power.
Edward and Eleazar explain Renata's power to Bella and make comparisons of their powers. During the confrontation, she clings her hand on Aro's shoulder, ready to repel anyone who wants to harm him. Fortunately, her power remains necessary.