... As long as you don't go getting on the phone to every female relative you and DD share to tell them the 'good' news!! My mum did that to me (oh, and after she called my nanna and aunties, she went all over town bragging to her workmates and 'friends' she bumped into at the shops, wtf?!) and it was HUMILIATING. Seriously, the bleeding bit I could handle. Having the whole town know exactly which day I started getting my period, was the part that sucked.
I think you feel weird because hey, your baby girl is growing up! I find it really scary that girls these days are starting to get AF at such young ages - I personally was nearly 15 when mine started, and had been convinced for two years that I was a complete freak because all my friends had theirs and there must be something wrong with me. (And that made it worse when my mother told everyone about it, I was a 'late bloomer', you know?)

But yeah, I think the weird feeling you're experiencing is mostly just grappling with the fact that your little girl is growing up... the thought of our kids being able to make their own kids is frightening when they've finished school and working, let alone when they're not even out of primary school yet!! It sounds like she's coping okay with everything, which is good My only advice would be to keep the lines of communication open, check in to make sure she's dealing with the inevitable cramps and mess alright, and try not to feel bad about 'missing' this milestone - I'm sure your DD isn't at all worried that you weren't 'there' to help her, if she was prepared and aware of what was happening, she should be fine
*hugs* Welcome to puberty, eek!!!