Oh goodness. What a tough position to be in as the grandmother. There are two things here that I must say---------- first, they've told you that they are not actively seeking your input on this situation. That is hard --------- you love her and them and want to help. But you must tread lightly so as to not create a situation that makes them defensive.
Now, the second thing is that I agree, some of what you have written is concerning. It is absolutely true that kids develop at their own rate. Many kids walk late. There is an old saying, those who walk early will talk late and those who talk early will walk late. She was a little off with both. But . . . as they have told you, not enough of a red flag has been raised for the pediatrician to want to act on it. If I were the parent, I'd ask for an evaluation by a physical therapist. She may have low muscle tone which they do fabulous work to improve upon or she may have motor planning issues and has a hard time coordinating muscle movement. This would explain the lack of understandable words as well. (motor planning involves muscles (dyspraxia when a child has significant issues with motor movement and apraxia when a child has significant speech issues)------- a physical therapist, occupational therapist and speech therapist all work on motor planning issues. By law in the US, if parents or doctors have concerns about a child's development, based on income----------- evaluations and services are provide for free to families under federal and state grants. It is the birth to three early intervention program. I'd have her evaluated if she were my child only because------------ well, why not? Better to do that and find out nothing is wrong than to have her need some extra help and not get it.
But, she is not your or my child. She is theirs. Some parents have a difficult time saying that something might be wrong and they wait until they can no longer deny it. And a small problem can cause missed milestones. A small issue can go under the radar for a while-------- and then blow up later. Early intervention can solve some of these issues and often quite easily. Again though----------- your son or daughter and their spouse must come to this conclusion theirselves and you just be supportive and helpful when they do.
Now hair pulling------------ just pulling out hair is a sign of ocd. OCD is under the anxiety umbrella and is a chemical imbalance. Eating it falls under the category of PICA which is under the same umbrella. This definately should be discussed with her pediatrician. Eating hair in humans (unlike cats and other animals) is dangerous. We can not digest a hair ball and it can block the intenstines and require surgery. For a child so young, I do not know what the course of therapy is. Some do believe it can also be caused by a vitamin definciency. I think if this were my child, I'd look into that avenue although in adults, PICA usually requires psychiatric care. Does she have a limited diet? Anyway, her parents do need to discuss the hair eating with her doctor as that is dangerous.
good luck
May I ask who looks after the child during the day is her mom a stay at home mom or is the child in daycare ? The talking may just be a little late but the hair pulling out could be a sign of being upset, has her pedetrician checked her out?