Even though it hadn't been that long since she came back to the land of living, Soura had seen the worst to make her regret her decision to pass through and one of them being the death of her lovely son Stuart. She loved her last born with all her heart, Stuart was her favorite and that's why somehow she did everything to protect him from the curse.
When she was approached by her ancestors on the other side, she had to choose between her three sons who would be punished for her wrong doings, for tapping into the darkness and create vampires - and she didn't hesitate to save Stuart. There was no asking twice who her favorite son was, that was well known for even amongst the first species themselves.
So she made a promise to avenge him, and there was no place she would seek help that to Gladys - a witch who brought her back. Hence she started finding her to see of any possibilities available.