A strong female werewolf from another pack could be a great love interest. She could bring a different perspective to Derek's world and they could bond over their shared werewolf experiences. Their relationship could be about uniting their packs in the end.
Maybe a girl with healing powers. Derek is often in dangerous situations, and having someone who can heal him would create an interesting dynamic. She could be gentle and kind, which would contrast with Derek's more brooding nature, and that contrast could make their love story really engaging.
A character who is a psychic would also be a good love interest. She could understand Derek on a deeper level than most, being able to sense his emotions and the turmoil within him. This connection could lead to a very intense and passionate love story as they navigate the challenges of his werewolf life together.