Fuyu told her about there relationship as Susan remembered that. Although it's a common practice if one woman wasn't lactating they can asked those who were and ask them to take care of there kids with some resources or Kuri in return. But Susan didn't just do that for the love of her son, of course it was there but something more was also in Susan's mind as she used to like it when he suck on her nipples like leach it made her feel something amazing she can't explain to others that's why she secretly kept on doing that.
