My 14 month old baby for the past few weeks has been peeing her dieper full atlest every 30 min.what could cause this?

Could be diabetes : Diabetes insipidus is a condition caused by inadequate secretion of ADH (vasopressin) (anti diuretic hormone). Affected individual cannot concentrate urine even in dehydrated state. Have her checked by her pediatrician.

Large urine volume: Several issues may be causing this, including giving excess fluids and even diabetes. Speak to your pediatrician for evaluation.