The best gift for a mother-in-law on Karva Chauth would be something that shows your love and respect for her. Consider thoughtful options like a personalized photo frame with a cherished family picture, a spa or wellness voucher for her relaxation, or a beautifully crafted piece of home decor. You could also opt for a heartfelt handwritten letter expressing your gratitude and affection, making her feel truly special on this auspicious day. Ultimately, the key is to choose a gift that reflects your appreciation for her role in your life.