I am an only child, I had a really happy childhood, friends to play, enjoyed and learnt to play on my own and never felt lonely.
I really can enjoy being on my own and enjoy my own company because i learnt this as a child.
My dad did lots of boy type things with me, not cos he wanted a boy just so that i didn't grwo up thinking that i couldn't do boy things. I learnt to put oil in the car etc and pump up the tyers on my bike, press the acelerator when he was fixing the car
Siblings dont always get on, dont like each other and grow up to never really like each other or ever spend any time together.
As an only child you can pick your friends, never have an annoying sister borrow your stuff, or an annoying brother stuff spiders down your bed.
I had lots of friends growing up both boys and girls and sleep overs etc with lots of fun.
Christams was great fun and although not spent with other children i never knew any different did I? I had fun playing with toys and board games were played with adults - my dad never let me win either.
Your dd will not know any different and what you havn't had you will not miss.
Play dates, sleep overs a social home and she will grow into a kind sharing girl.
enjoy your dd