When is it someone else's place to suggest a child may have special needs?

Someone I know (family member of a close friend) has a child that is in my opinion showing many signs of needing an evaluation/ concerns brought up to a doctor. My friend also feels the same way and asked my opinion about it but the mother makes excuses and ignores everything.

The child turned 4 in March and is still wearing diapers, and when she doesn't she will just look at you straight in eyes and piss her pants and laugh. She JUST started talking a few months ago and when she talks you can barely understand what she's saying she babbles and is barely coherent. She completely lacks comprehension if you talk to her and ask her to do something she stares straight through you and won't do it, or she will just have a blank empty smile and say "ok" but won't follow the direction or answer the question. She can play with other kids but is super aggressive and doesn't take in any social cues from other kids at all. She randomly screams and shrieks , not in an angry way but a very random excitement noise at times that seem inappropriate to do so , like nothing is exciting her she's just making these sounds.

Mom doesn't want to hear anything from anybody and keeps saying she's fine. Is is inappropriate for family members and friends to kindly bring up concerns or is it completely inappropriate in any case ?