Jane Foster is Torunn's mother, and this is the true reason she was left on earth.
It is assumed that Torunn's mother is Sif as she is Thor's wife in Norse mythology. It is also noted that Thor's decision to abandon her on earth to teach her humility like his own exile did is misguided as he needed that lesson only because of Odin's poor parenting.However it is possible that Torunn was actually Thor's daughter with Jane Foster, or possibly another Midgardian. Under these circumstances it raises another possible motivation for abandoning his daughter with Tony, it is possible the Asgardians wouldn't accept her as a half midgardian, particularly perhaps if Thor wasn't married to her mother, even more so if he was married to Sif.
His excuse when he finally speaks to her again then? A comfortable lie, one that she was too excited to see through at the time. As for saying that she would be welcome now... well perhaps he had the time to bring them around in that time.
- She has also proven herself a brave and honorable warrior, which would win her more respect points with the Asgardians than a literal babe in arms would get.
