I'm not sure where to begin.
The child's rights are covered under the IDEA (Individuals with Disabilities Education Act). It is a federal law. States may interpret it differently, but they can only offer more services/rights, not less (yes, they don't always folllow the law).
If the child is under three, your friend would need to go through the early intervention program in her area. If the child is three or older, your friend needs to contact the commitee on preschool special education chairperson in her school district.
Have her do everything in writing and keep copies of all correspondence and keep a journal/log of all communications. In her letter, make sure she requests an evaluation, and that she indicates that she knows that they only have 60 days from the receipt of the letter to perform the evaluation, hold a CPSE (committee on preschool special education) and determine the appropriate program (again, this is federal law...this part of the law is often broken).
Make sure she knows the term FAPE (FREE and appropriate education). It's every child's right and is protected under IDEA. She should not be paying for any services her child needs.
It is imperative with autism, to receive early intervention. The earlier the therapy starts, the better chance for a positive outcome.
A few other terms she needs to know is LRE (least restrictive environment), Needs, and Appropriate. Make sure she never uses the word wants, always use the word Needs. They don't care what she wants for her son, only what he needs (it's semantics, but they will jump down her throat if she uses the wrong word). Never use the word Best, always use the word Appropriate. Her child doesn't have the right for the Best education, but he does have the right for an education that is Appropriate for his needs.
If she doesn't agree with the outcome of their evaluation, she can request an IEE (Independent Educational Evaluation) at school district expense. They will probably say no, but then she can request an impartial hearing.
A 504 is covered/protected under the ADA (Americans with Disabilities Act). It is for children who have a documented disability who are succeeding in school without actual special education services. It allows for modifications, both physical and academic, that the child needs.
Please feel free to PM me and ask any questions that you or she may have.