What could be the cause for my 19 month old to have stone like stool? and what can i give her to easy her pooping or stool

Hard to guess: Each child with constipation needs to be sure there is no other disease causing it. A pediatrician's evaluation is needed. We do not want a child to get chronic constipation. If constipation is due to slow movement of food and poop through the gut, then things to try are vegetables, water, prune juice, prunes, fiber-plus-water, Miralax (polyethylene glycol), senna extract, milk of magnesia, etc...