Suggest Treatment For Speech Disorder In A Child

My daughter Priya is 10yrs old.She is a slow learner.we get her assesses at NIMH every year and the recent report says she is having mild retardation and her i q level is 51 % her social maturity is almost 50 % but her academic level is 20 or 25 % her main problem is she is not enabled with clear speech there is no cleft palate problem or valium problem I need some suggestions to improve her speech I have tried with several speech therapist till now but bank of words have improved she has a lot of work I believe she is able to understand instructions to some extent even complex instructions also she can understand but she is not able to answer clearly because of the lack of proper Speech can you please suggest any good idea on how to develop the Speech thank you