When River Song first meets Donna Noble she is taken aback by the fire the woman burns with. There is more than the red of her hair that makes Donna Noble glow and shift like the surface of a new sun. There is the warmth of her goodwill as she sheds a tear for Miss Evangelista, someone she barely knew. The scent of her perfume is spicy, mixed with the crackle of TARDIS energy it burns her lungs as Donna breezes by. The sizzle of her back and forth with the Doctor, not River's Doctor, not yet and never completely. Watching them together now River can understand how it is she never had all of the Doctor. He loses a piece of himself to each of them but they give him so much in return, Donna will want to give him her everything and he will be forced to take it.
River cannot help but smile when she finally meets Donna Noble, a smile as bright as the fire the woman before her burns with. As bright as the fire burns River cannot help but want to weep. She cannot help but want to grab Donna and urge here to run, she wants to be able to do anything other than say the word she's so tired of saying. She has no choice but to say it anyway she knows and just hopes her voice doesn't break as she does. Knowing what she does and River knows so much, too much, she knows the brighter a person burns and Donna burns so bright, the faster and more suddenly they must fizzle out.