My daughter is nearly 12, and I understand what you are feeling. Sometimes it is harder for mom to let go than anything. Remember the 1st day of school? She was totally excited and I sat in the car after dropping her off and cried! It goes like that all along, right?
What we've done is to just hang out together. We go on a few expeditions, like shoe shopping at Payless. She gets a kick out of the fact that we wear the same size, and we try on a bunch of shoes before picking one pair each (this was when we needed shoes). Or even just to the grocery store. My daughter got interested in cooking a couple of years ago, so she's also interested in helping buy the food. But it's not so important what you do as that you do something together. Just don't make it a big huge production.
I like to give good-night hugs and tuck kids in when I can; kids are usually okay with these sorts of things when friends aren't around. I tell her often that I love her and that I'm proud of the choices that she's making. I get lots of hugs back, too. I have told her (jokingly) that it's a mom's job to embarass her kids from time to time! She has a good sense of humor and we can tease back an forth. It's all these little things that make me feel comfortable with her growing up and moving into more independence. When she needs someone, she'll come to me because we have (all along) had a pretty good relationship.
Do make sure that you know all her friends that she hangs out with! Friends can be a big influence on each other, and who she hangs out with can really affect her attitude, behavior, and self-image as she grows up. When parents take the time to get to know their kids' friends, it also helps parents feel more comfortable with kids being out, and helps the kids stay connected still. And if you know the friends moms, you can maybe do some mother-daughter things together.
I don't know if I am helping any ... hope what I say at least makes sense!