Doesnt speak clearly like 3yr old, 2 syllable words are difficult.she mumbles on and i can't understand most of the words.should i be worried?

Yes: At 3 a kid should speak clearly enough for 75% of his/her words to be understood by a stranger. If this is not the case you need to seek out the "child find " program run by your local public schools. They are mandated to seek out and treat kids with identified speech/language or other deficits in the preschool years to prepare them for school entry.