You'll be OK if you can have your daughter evaluated by a
speechHearing or speech impairment - resources
Speech disorders and language pathologist who specializes in the pediatric population. The clinician can determine your daughter's status in relation to the development of speech and language, and determine the appropriate therapy regimen to addres any difficulities that may be found. The relationship to hypothyroidism need not be central to the matter you're investigating. In other words, the key is to determine if there are any abnormalities and to attempt to remedy them. That course will be true regardless of the causative factors, at least in a general sense. Start with the basics and go from there.