Not so good—You'll feel better soon。
不要说：你马上就会好的。

This is a presumptive thing to say and it's more for your benefit than your friend's. You wanther to feel better because you hate to see her suffer. Make sure you don't dismiss her grief.
这是个假设句，实际上是从你的角度出发而非你的朋友，因为你不想再看到自己的朋友沉浸在痛苦之中，这样你自己也会好过点。但是别忘了你并没有减轻她的伤痛。

Better—I'll be here for as long as you need me.
不如说：只要你需要我，我就会一直在这里。