Dehydration is the most important factor indeed. I guess vitamin c supplement is a risk for a person who has a history of calcium oxalate stone. Upper intake level in those cases in about 1000mg and most of the vitamin C supplements contains 500 to 1000 mg which makes it a potential risk if they are consuming it in high doses.
But obviously, proper hydration is needed.
Thank you for your comment, I appericiate it !!