How to cope with exchange student leaving?

I am a 16 year old girl, and my family and I have hosted an exchange student this year (she is a 16 year old girl like me). It was my idea to have her here, and I was the one who convinced my parents that this was a good idea. I have one older sister, and she left for college this year, so it worked out to have the exchange student move in so I wouldn't be alone all the time. We have become very close, and I have learned a lot from her. It has been wonderful to share my life/culture with her, and vice versa. However, I have been her closest and only true friend this whole experience. She is extremely shy at her school and has made almost no friends and never goes out to do things. Unsuprisingly, she has gotten just too homesick and is going to return to her country in 4 days. Just a week ago, everything was fine, and then I get one text from her out of nowhere with this sprung on me. She never considered how I feel about this...she is very clearly thrilled about going home and giddy with excitement, while I've cried several times about it. I just have so many emotions- anger at her for leaving me, sadness that I may never see her again, happiness for our good memories yet disappointed at how this all ended. I never expected our first time hosting a student to end up like this, and I could really use some advice from other host families. I know that it's her choice and I am respectful of her decision, but I just need some closure on the way this all had to end.