This is a genuine question as I really don't know if I'm being fair to her. I fear she's letting her DD down, and I don't know what to do, if anything.
Background: I had Dd1 6 months before she had her DD. Mine is totally normal, by which I mean good at some things, awful at others, very charming. According to my sister, MY child is a genius and amazing. In fact, my DD is neither (though I love her, obviously). Her cousin, sister's DD, is way behind her in development, and way behind her peer group, which is what actually worries me. I know children are all different and it's not one thing that worries me; it's all of them together.
She didn't move much as a baby - sat at 10/11 months, I think, walked at 20 months but reluctantly, seemed lost in a fog all the time. She was hard to engage - never looked at where you pointed, never noticed much, never played with toys for long or creatively. She has never played a game with me - not even peepo. She's nearly three and has a vocabulary of maybe 50 words, a lot of which are numbers, colours and animal noises, which my sister has taught her practically since birth. She can sing nursery rhymes without pronouncing the words properly (so I think doesn't know what she's singing) and otherwise doesn't speak in sentences at all. She still doesn't walk brilliantly. She does do role play games (pretending to cook etc) but doesn't play with her dolls to act out situations or play imaginatively. To me, she seems more like an 18 month old than a three year old. She doesn't understand basic instructions and certainly not two-part commands. She's prone to bad temper and lashing out but most of the time she's sunny and sweet, although still not engaged with her world. The temper could be frustration at communication problems but she has always been like that, even as a very small child.
I've repeatedly hinted/said to my sister that I would talk to their GP if I was her to rule out hearing or sight issues, at least, as she was slow to walk and now talk. (I get on with her well and it wasn't taken badly but it was ignored.) The health visitor told her not to worry, which is now gospel, but I suspect my sister didn't give her the whole picture as she was more asking about tantrums than development and at the time her lack of speech wasn't all that unusual at that age, but she hasn't improved since. Now she is insisting her DD is normal and mine is just very talented, which is not my point, or true. Sister works full time and lives in an area where it's hard to meet other mums so I think she just doesn't have anyone to compare her DD to. She also has a real Pollyanna approach - if she thinks everything is fine, it will be. This is how she deals with life, not just motherhood. My niece has a nanny, who is too professional to discuss her with me, not that I would ask her to, but from things she's said (desperately hoping sister would take her to the GP to discuss development) I infer she is concerned too. My brother- in-law is equally busy, unfamiliar with children, glass half full. They both think she is lovely but thick (and say this in front of her 
).
I love my sister and niece; I'm very worried that my niece has some delay that could or should be picked up and treated. I'm not a doctor. I don't know much at all about it. If she was my child I would have dragged her around every health professional I could find to make sure I wasn't missing anything, and I'd have done it years ago. I'm frustrated with my sister but for my niece's sake. And I may be being paranoid. My DD is clouding the issue as I think my sister feels I'm unfair in comparing them, but I don't expect them to be the same. I do see children the same age as my niece all the time, and my niece is nowhere near them, or children much younger. Her own sister is 11 months old and sharp as a tack - walking already. Yet no alarm bells are ringing for my sister about her older child.
Thoughts? Suggestions? Reassuring anecdotes? Biscuits?