Oh i feel your pain!
I know it will be hard and so upsetting when she goes, but there are many things you can do to still feel close.I know its not going to be the same as in person but here are some things to think about:-
1) Down load a thing called Skype. Its free and easy to download.Buy a cheap mic and cam for your computer. Then you can see each other and talk in real time like a telephone, except you can see them. Arrange a set time each day or week to catch up with each other.Soon, you will accept she is gone, but feel like she has'nt because you can see and speak to her still.
2) Put a bit of money away each month, so in time, maybe when she is settled, you can go and visit.How fab that reunion will be!
3) Send text messages on the phone.
4) Send funny cards with messages in it.
I know i am probably not helping much now, as you will feel so sad.But i hope in some way it makes you think.So many solutions to this.You are not alone and i think your friend will be feeling the same you know.