The reddening of the comb and wattles is a good sign her time is coming soon. Their size is just part of genetics and shouldn't change. Sometimes they will start "squatting" when they are about to start laying -- they drop to the ground and spread out a bit, maybe raise their tail a bit -- actually the stance that tells the cock it's OK to mate. Sometimes you will see a little pinkish color on the legs and feet, due to a rise in hormone levels.
But in the end, each bird is an individual, and they will lay when their system is ready.