Sister making things up about DN

[CarrotCakeandCoffee]

My sister is extremely opinionated about other people's DCs even more so since becoming a mum herself (whereas I would think most people are less judgey once they become parents).
In particular she is obsessed with other toddlers/ babies development, milestones etc and actually very critical! I've lost count of how many digs I've ignored about my own DS being behind for his age! She actually caused a lot of anxiety when my DS was younger and as a result I spent so much time worrying about him but as far as we aware he is NT from being checked out as she made me paranoid!
Fast forward to now she has a DD whos 18 months who she claims can walk independly and is very chatty. However every time I have looked after DN or my mum she has never walked or talked and as far as I'm aware no one has seen this happen apart from my sister. I'm not saying this is a bad thing but I just don't get why my sister would over exaggerate or lie?
Her recent obsession is a family friend we know who she claims is delusional about her DS who's only about 7 or 8 months and she thinks there is something wrong with him developmentally. How would you navigate this?

you don’t seem to like her very much

any reason why you have so much contact with her?

She might be worried about her own child's development but is trying to project to everyone that they're ahead or on track or whatever. Some people can be very strange about milestones, like their kid is superior because they're an early walker or talker when in reality they're all on their own path. Can you have less contact?

Thank you for your replies. I love my sister but there are qualities about her such as the above I don't like. I suppose I chose to overlook certain behaviours for an easy life. Plus I love my DN and want to have a relationship with her too as well as my DS. But I think I'm going to have to take a step back as I'm finding her more draining. She's very competitive and will always put a negative spin on things. For example, we live in a more affluent area than her which she hates, so she's forever making digs about the school not having quite as good a reputation. as the one closest to her (not true) and questioning that we must be skint to afford our house to live here and she would rather have the extra money for activities for her DD ( we aren't struggling and we don't live in a really expensive house!) But you get the idea.

she sounds ghastly and not someone i would want to be around, let alone my child

We had a similar situation years ago is DSIL and DMIL making things up about DN. I have no clue why. It was things like she was sleeping through when they both knew we were having sn horrendous time with DC1's sleep, absolutely on our knees at the time. DSIL told me years later that DN didn't sleep through a night for years.

I have no idea why they did it, maybe a feeling of insecurity because DN was behaving typically in a few ways.

I would try and keep up your relationship with DN but try not to rise to any comments that your "D"Sis makes about your choices or your LO

Sounds like a weirdo tell her to get a hobby

My first thought was that she has deep sense of insecurity. Does she have any diagnosis?