My daughter is 9 months and she can't poop what should i give her?

CONSTIPATION: If breastfeeding, continue, give more water, increase fiber in the diet like more vegetable, oatmeal cereal, prune juice 3 ounces x2/. If formula fed, may try whey protein containing one e.g. Garber good start; this will increase the bulk of stool, make stool mooshy. If doesn't help, give MiraLAX (polyethylene glycol) 1 teaspoonful twice daily mixed with 6-8 ounces of formula, then may continue once daily as needed.