Is not treating autism child abuse?

A close family member of mine (by marriage) has a son, who is nearly four years old. He has CLASSIC autism spectrum signs. He is nonverbal, excessive stimming (circling for hours and jumping repetitively for hours ln end), transition issues, behavior melt downs, and will not make eye contact. I grew up in a family with many autistic children, and direly want the mother of this poor boy to have him tested and get him services so that he can excel to the best of his ability. However, she is in blatant denial that there is any sort of neurological behavior going on here, and says it's just his personality. I feel like this boy is missing out on alot of services during his developmental years that will help him have a mich easier life. Uit it is impossible to have a conversation with the mother as she jumps to defensiveness immediately and shuts down any conversation. Has anyone else encountered this? How does one help a child whose parent refuses to help him? It's so sad to see him feeling so frustrated and confused in his own surroundings day in and day out.