I can understand your depression. You love your daughter, she's also been a great friend to you, but she too needs to move on with her life. She said she is looking for change.
Surely, you're going to have to have some grieving time, but that is typical for any mother to see their child moving so far away from them. But this is something that she is excited about and is looking forward to the change.
Try to be encouraging for her. She needs your support as well. I think by her givning you the red pin, it was her way of saying to you that she wants good things to go on for you too! She is letting you know that she thinks this group is wonderful for you and she would like for you to continue to be part of it. Maybe that's her way of making sure, you'll be finding new changes in your life as well.
And remember, there are also phone calls that can be made, "just thinking about you cards" with little notes inside to send in the mail. And you said it isn't that far, so maybe you two could make time for a visit here and there and spend some quality time together.
So for me, grieving this transition is normal. Be strong, encourage her, and let her know she will be missed but you look forward to some of the suggestions given above if they fit you.
When my daughter moved out, she said it made her so happy to hear that I was out and about doing things. She said she was glad to hear that I wasn't just sitting at home moping around. It relieve her and allowed her to be truly happy. I grieved, but I'm better with it because I know she is truly happy, moving on with her life.
Give it time, I hope it gets better for you.
Update us after your social. I'm curious what goes on there.