The Arbiter could be a great character to pair with the female Master Chief. Their different cultures and combat styles could create an interesting dynamic. Another good option could be a young UNSC engineer. The contrast between her combat skills and the engineer's technical know - how could lead to some great story moments. Also, a fellow Spartan, maybe one with a more light - hearted personality, could be paired with her for some buddy - cop - like adventures in the Halo universe.
One character to pair her with could be Cortana. Cortana's intelligence and strategic thinking combined with the female Master Chief's combat abilities would make for a powerful duo. They could work together to solve complex problems within the Halo rings. Another good character would be a Covenant Elite who has defected. The female Master Chief could initially be suspicious of this Elite, but as they face common enemies, they could form an unlikely alliance. And a UNSC Marine with a lot of battlefield experience could also be paired with her. The Marine could provide a different perspective on the battles and situations they encounter.