hi, im an older mum too (43 with a 2 year old). I have similar worries. She is an only child and having older parents who themselves are a bit loners, keep themselves to themselves and aren't really into the stuff everyone else is (never listen to radio 1, don't wear make up) and I worry where my daughter will learn to be a popular kid, rather than the oddball on her own in the corner as I find it hard to make friends at groups. I go week after week and everyone seems to be friends, but no-one really talks to me and I don't like to really impose myself on people.
that said, I think I realise that these are my issues, and my anxiety, if I don't keep it in check, WILL rub off on her and give her issues!
I doubt that your daughter has been bothered by the xmas cards thing (it would have bothered me too btw).
I think the right answer to 'do I need to care anyway' should be NO. You are what you are, and your daughter loves that person (and she's the one that matters).
How to widen the circle.... when is your daughters birthday? can you have a party? maybe you could host an 'aloe vera' party( do you know what I mean, you get the 'forever living' rep to come to your house with loads of samples. I went to one recently. one of the ladies got a face mask, I got a wrap done on my arms, free samples were given out. as a host you put on some nibbles for everyone) and invite some of the mums somehow? would the nursery allow you to distribute invites?
or perhaps look up your local NCT 'bumps, babies and beyond' group. they usually organise regular socials and might be able to point you to some weekend socials.