my girl is almost around 26 months, also 1 poo poo in every 3 days. Very hard one & she is so scared when she get the need. I started giving her some honey to drink every day for about 1 week - the poo poo are softer now & can have it in every 2 days. Perhaps you can try.
2 teaspoon of honey with about half cups of water. I think kids love to drink honey as it is so sweet.
Of course it's not magic, you need to keep giving her to drink at least a few days to see the results. Besides, really need to increase her fiber intake, like fruits & veggies. cut it really small & blend to the rice , congee.
Smartest,
just a reminder to give your kid more water to drink if you give your kid 維多c to drink. Vitamin C is water-soluble. if intake too much without water, may cause kidney problem. I am not sure if half tablet of 維多c is ok for your kid or not. But if nothing special & if you don't like to drink water, I think you better not to give your kid to drink it every day.
Really understand your problem. keep on trying to mix honey in the milk. it really works to my girl. she can now have poo poo every 2 days & softer one. She used to have it once in 3 days & very hard one.