I have no experience with a child with constipation, but I would...

I have no experience with a child with constipation, but I would guess it should take a couple of hours to work thru the system
are there no instructions with the medicine ? as to say how often or when a double dose can be given

some foods work just as quickly, a couple of teaspoons of tinned tuna in spring water for example....

freshly cooked cauliflower is another

they can work in an hour or so
hopefully other members will be more cluely
I really cannot recall my children ever experiencing that problem
have a look at her diet and what she ate for the past couple of days
we do have some good food gurus on this site so hopefully they see your post
cheers