Shmi lived and when Ani became Darth Vader he still wanted her around. He also discovered that his children survived, and installed Shmi as their governess, trusting her completely with his children, and promising they wouldn't be taken away at a ridiculously young age.
Shmi being an awesome, and willing Grandmother to Luke and Leia, even in her basic imprisonment. Maybe she actively sways them against the dark side, or realises that she really doesn't need to.
Bonus:
1. Vader attempting some level of affection for his mother even if he can't say it; giving her official titles, amazing clothes and apartments and an actual say in a lot of his children's schooling as well as expecting all the officers to treat her with respect. 2. Vader doting on his kids as much as his mother.
Gen, Shmi survived, Vader makes her care for his kids, angst, feels
Shmi being an awesome, and willing Grandmother to Luke and Leia, even in her basic imprisonment. Maybe she actively sways them against the dark side, or realises that she really doesn't need to.
Bonus:
1. Vader attempting some level of affection for his mother even if he can't say it; giving her official titles, amazing clothes and apartments and an actual say in a lot of his children's schooling as well as expecting all the officers to treat her with respect.
2. Vader doting on his kids as much as his mother.