What have you got to lose?
On one hand, friendships last forever, and if you solidify and hold on to that, it will always be there for when you come back on leave.
On the other, if you make something like a relationship into it, it could either go well or end up with both of you in pain. Also you may not have anything to come back to.
Talk to her about it, just probe. If she is your best friend than she will understand you.