Hi, I have two ideas.
1) Hayley was cursed into a wolf for some reason and can’t approach Klaus/Hope since Hope was young or her birth so Klaus was raising Hope. However, she can watch them from afar so she does. Klaus doesn’t realize Hayley has been watching them but Hope does and doesn’t know who the wolf is, but feels a bonds and knows that the wolf has been watching over and secretly protecting her.
2) After Hayley left Mystic Falls, someone kidnapped her to take Hope for her power. They trapped Hayley somewhere until she gave birth, then took Hope right away and left. However, no one realized Hayley had twins and actually gave birth to a son after. Soon after the kidnapper(s) took Hope, they encountered the Mikaelsons who defeated them and Klaus raised Hope, who grew up being like Hayley. Hayley raised the son (perhaps Henrik) who grew up being like Klaus, but also never stopped looking for Hope. Even though Hayley looked for Hope and Klaus looked for Hayley, it was Hope and Henrik who found each other, not realizing they were twins (or they can) and tried to get their parents to be together.