I've only saved a couple of squabs in springtime, but with the weather being cold at present, if you can find a cardboard box and line it with an old towel and move her into it, continue to feed and water her she might make it (a little bit of fat mixed in with the rice or bread too).
Hopefully someone more knowledgeable will point you in the right direction, but remember they are sky rats to most of us allotment peeps and you might not get a lot of sympathy ;)
Ninny