Vada did like Shelley, she just didn't like Shelley being with her Dad. Vada was jealous because she was struggling for Harry's attention and he never had time for her, yet he was able to make time for Shelley. Vada understandably felt jilted and her dad couldn't see that, so Shelley was the only one to whom Vada could show her bitterness. It was really Harry's fault for being too oblivious to see that his daughter was a child who needed his love and understanding. He thought she should see herself as a mini adult who could handle anything on her own.