Concerned Mom of a 3yrs old

My daughter is 3yrs old and 7months but she can't speak simple sentences. She had a hard time pronouncing some words. But she can understand instructions its just she can't compose straight sentences. Sometimes when we have some visitors she doesn't pay attention when our visitor ask her what is her name, she just do whatever she liked to do. But if both of us were alone in the room she will answer immediately if i ask her what is her name. What should I do? #firstbaby #1stimemom #advicepls #pleasehelp