Hi I am a speech-language pathologist. Since your daughter is 4 years-old, you can call the local public school and ask if they offer preschool screenings, evaluations, etc. Once a child is three years-old, they can attend the public school in your area and receive speech therapy if appropriate.
There are some sounds that are devlopmentally appropriate not to have when you are 4 years-old, a few of them are R, L and TH for example. You also have to consider if people understand your child when she is talking. You can ask her preschool teacher too if she has any concerns regarding her ability to be understood by adults and peers.
My school district offers a preschool screening five times per year. You can call your local school district and ask if they have that service just to make sure her speech is developmentally appropriately. If they do not offer a preschool screening, then ask to speak to the speech-path and tell her your concerns. She will be able to tell you the specific protocol to follow in your area. This is a free service.
If you go outside of your school district, it can be very expensive.
Hope this helps