I'm sure she feels terrible for Ed Balls losing his seat, but if, as has been reported, they both have (had) ambitions to lead the Labour party, his being removed from that particular picture will avoid any Miliband-brothers-style leadership dramas in the Cooper-Balls home.
FWIW, I've been impressed by the way Nicola Sturgeon and, to a lesser extent, Leanne Wood and Natalie Bennett have been performing as party leaders. I think Yvette Cooper could be the new broom that Labour badly needs.