toddler constipated

i noticed for a few weeks that my daughter of 2 1/2yrs old is constipated she would have a bm every 3days, her diet prior was bad foods...and i am sure that is what caused it, because she was never liked this with being in my trimester and my sciatic nerve hurting and being in pain i chose the easy route and have the kids eat frozen dinner meals....so now we are putting better foods into her system...rice/fruit smoothies/fruits/making fried shrimp/chicken....just the broth with rice...but she is still backed up, so i ordered dr.schulze's intestinal formula #3....how long should a child her age be on a bowel cleansing formula and what is a good probiotic brand for her to take...i am highly considering giving my daughter uny's intestinal formula #1 until i receive her's...i have suffered from constipation so i know it does not feel good...

vk