Arabella had always tried to lead an ordinary life or as ordinary a life one can lead with a Phd in psychology at 17. Not to mention the fact she is aware of the supernatural due to her unique circumstances but she tries her best to live her life blissfully unaware. However, her normal peaceful life is destroyed when she tries to stop Elena from being kidnapped the night of the masquerade ball. Meeting the Mikaelson brothers definitely wasn't on her to do list but she wouldn't change it for the world.
Klaus and Elijah have fallen in love with multiple women across their lives, but none of them could even compare to what they felt with Arabella.