That must have been really upsetting to see, especially since your grandson put real effort into knitting those for sick kids.
I can’t tell what you mean by “karma came fast,” but in situations like this, it often helps to focus less on that idea and more on what actually happened and what can be done next. If your daughter-in-law threw away something meant for patients, that’s a serious disrespect of the gesture—and it could be worth addressing directly when things are calmer.
If you want, you can tell me what happened afterward or what “karma” you feel followed—I can help you sort through it or figure out how to respond to her in a way that protects your grandson and avoids more family conflict.