Of course now that you are ready, they aren't! :/
I have noticed that with broodies that I hold off, it takes longer for them to recover. I think it is simply a matter of how much energy and nutritional stores they use up in the process as a hen's body has to be at a certain level for the hormones to kick in again. It could also be genetically hormonal, and as the hen ages, her hormones never get high enough to brood again. But let's not assume she is a one timer gal yet.
I read somewhere awhile back that there has to be a certain amount of calcium in their body levels to brood, and supplementing with calcium can encourage them to brood again. I tried that with my Silkie after she had been having a string of broods, then a big lag, and it worked. May have just been coincidence, or there may have been some science behind it.
So supplement her, if you aren't already, with some calcium grit. Put her on a good higher protein level layer feed. You might worm her and check her for body parasites as brooding can definitely encourage overgrowth in those areas. I like to use Rooster Booster Triple Action Multi-Wormer (mouth full, but it works). It is a wormer with FDA approved meds for laying hens as well as vitamins/minerals and probiotics. It comes in pellet form that you add to the feed. All the chickens can eat it. I get the best price at http://www.abetterchicken.com/product/50101.
Give her a good dusting with Poultry Dust. Set out BOSS, ACV in the water...in short give her a little spa treatment. If she is laying again, breeding, and glossy feathered, plump, happy, warm and has a cozy nest, you may have a good brood as reward, espeically as the spring time warmer weather is approaching.
Good luck!
LofMc
Thanks so much! I've been around the bush and back trying to determine what to use to worm my birds. You're suggestion sounds right for me and my birds so thanks. Maybe she just needs the time to get strong again, as she was in pretty bad condition by the time she left the chicks. Thanks for all the great advice you give.