What if in the series Aunt Cass gets overprotective of Hiro because he's the only family she has left? Not to the point to make Hiro feel like running away, but the poor woman wouldn't want anything else to happen to her nephew and she'd sometime be a little invasive into his life, especially if she's not aware about his superhero life and FREAKS OUT when she learns.
She would be though! She wouldn’t realize how overprotective she’s being at first; she just wants to keep tabs on Hiro and make sure he’s safe and cared for. I think if Hiro still hasn’t told her about his superhero identity in the series, she would feel a little hurt that he’s keeping things from her. Lying about where he’s going at night (yeah, “studying with friends”) or keeping secrets about the villains he faces. If she had to find out on her own, she wouldn’t know whether or not to feel proud that he’s helping the city or disappointed/furious/scared that he didn’t tell her and that his safety is at risk. At the end of the day, she just doesn’t want to lose another nephew.