When bestie moves away

My daughter's best friend is moving across the country. They are 12 years old. She took it really hard and it is going to be really difficult for her. I can't stop crying, because I feel her pain and will miss them too.
They are moving for the similar reasons why I want to leave too. So I get it and it is making me wonder if I am doing the right thing by staying here.
My daughter really doesn't have any other friends that she hangs out with regularly and she just isn't interested in anything but playing on the computer. She has always been this way.
The day they move is coming soon and I want to be able to give her some good advice. Do you guys have suggestions?

I would say to her that she needs to stay in touch with her friend, by letters, or mobile phone, internet chat, Skype... you both could collect information on how is it there and, if it's good, also make further plans to go the same path.
I don't know how far is that place and if a planed visit is possible.
(sorry, I don't have kids so....)

Look at this as an opportunity. Encourage her to write - I mean actually correspond - and share with her friend. Is the new community close enough for your daughter to travel to? Would you be willing to allow her to do so alone? Many forms of travel have ways in place for unaccompanied minors to do so. What I am getting at is that giving your child something to look forward to might be what she needs to pull her out of the rut - even more so if they bear some of the responsibility for getting there. Start a work jar whereby she can earn through deeds and tasks the fare to do so.

Now, as for the moping about playing the computer. One, what are her responsibilities for such things? Again, I think earning time to do so is a worthwhile responsibility. Two, what extracurricular activities is she participating in? These are really important at her age. They give her something to burn off some energy. Hopefully she will develop interests beyond this friend. Art? Theatre? Music? Sports? Clubs? While yes these can require an expense there do in fact exist such things with little, no, or subsidized cost. In my case my son had a competitive talent for soccer which I simply couldn't afford. He was able to play on scholarship with a private club. Today that boy earns his living as a technical director for another club. Had I not done anything he would have sat around all day playing video games. Just pointing out the value of finding something to devote time and energy to.