What do you think I should do?

I'm 23 and she's 20 and we've been dating for 2months. She's leaving in 2 months for five months in the military and my mistake was i impulsively said during the middle of an argument "idk if this is going to work out." This sent her into sadness and made her cry. It made me sad too because she agreed. But, we've been trying to work it out since. But I asked her the other day if she wanted to keep dating. She said basically through many words NO. I wrote her a letter saying how much I regret saying something impulsively and through frustration and told her that her little xmas present would be arriving soon: small sensual lotion and purple (her favorite color) nail polish with a card and a certificate for "a romantic evening with a mage with rose petals, lotions and nail painting." But anyway, her mind seemed pretty made up. But, I told her to think about everything in aculation and that she should ask herself if this is what she really wanted. She's thinking about it now. Do you think there's a chance that she'll have faith this can work out? Do you think girls can change their minds once they have supposedly made up their minds? What should I do?