For EG we waited until she was a year old, and had her Simchat Bat at her birthday party. It made for a very, very long day, but it was quite an enjoyable experience, and definitely made it a special occasion for us and the family. We waited partly because we weren't ready, and partly because once we thought we were ready, both Grandma and my Aunt were dying, and it didn't seem right to be hosting a big celebration knowing they weren't going to be able to celebrate.
This time, we have lots of options. Typically there seem to be a few different options that are common:
1. On the 8th day. This is echoing the circumcision of a newborn boy, and really plays to the covenant aspect of having a Jewish child. Why wait if you can do it?
2. First Shabbat after Baby is born. This seems to be the most standard, and depending on the temple is either the Friday night service, or less commonly at the Saturday service. The family is called up to the bimah, and celebrated at the occasion.
3. Rosh Chodesh. Since this is a holiday focusing on women and girls, it seems to be a popular choice for a baby naming ceremony. It also gives a little more time to celebrate, but depending on where it falls might make for a mid-week celebration.
4. Any other time you want to. Since it's not a halacha ritual event, when you host it really means very little. There's something nice about establishing your own family traditions....
We haven't figured out what we're going to do. There's no chance of us doing it on Friday, since that would be tomorrow and we're totally not ready.
I'm personally leaning towards either doing it at about a month, or doing it when she turns 1 year old, like we did with EG.
Did you have a Simchat Bat for your daughter?