Doppelgangers are far simpler creatures, their only gimmicks are shapeshifting and giant hit if they catch you by surprise. But I wonder when and how she'll impersonate companions. Surely the real ones will have to be busy being elsewhere.
Or maybe she kidnapped one of them - the Monster Manual states that they sometimes capture the creatures they want to imitate, to study them, learn how they behave and talk, and that doppelgangers are even able to read (superficial) thoughts.
Maybe we could have some sort of rescue mission for a kidnapped companion.