Therefore, for Devki (just like in the original Devki's life where Krishna is her savior), here, Rads is Devki's savior. Hence the conflict of letting her go. She wants rads with her and cannot imagine her being married and leaving the house. She needs her for her own well-being as she is like a tender vine which cannot survive without some supporting structure.
Further, Devki is dim-witted enough to not know how to figure out an intelligent way out of the mess the entire radev wedding business has become. She will never be the one to divulge information but will have a breakdown and blurt it out! It will be a serious conflict of consciousness with Vishaka maybe having a baby or something with Dev or Rad being such a sacrificial goat that even Devki will be unable to sleep at night thinking of all the sacrifices a girl who is not even her blood is doing.