It sounds like you need to create a 'safe box' or broody nest area at ground level.... if coop access is the only problem then just make the hen a comfy location at ground level in the run for her to go at night. You can use a medium animal carrier or build a small box out of scrap wood.Okay, so I came home to find my hen had hatched out one of her eggs. She ended up leaving the other 3 eggs and took her baby out to forage for food. The baby was able to get down from the coop no problems. The other adults in the flock were curious, but the mom did a good job protecting her baby. I candeled the other 3 eggs and they were definately not developed right, and all obviously died during the incubation process. I came outside after dark, and I heard the baby going crazy. Apparently mom went back into the raised coop, and the baby couldn't make it back in. So I grabbed the little one and put her in with my week old chicks. Was this a bad move? The chicks seem like they are getting along together, and the day old is starting to eat and drink. I have a better way of ensuring that the baby is fed now without the adults knocking over the little feeders and such, too. I tried to move the mom into my grow out pen, but she went crazy. I am just playing it by ear and hoping for the best.
Coop access and night time nesting are frustrating with broodies but to me it is a trade off for the reward of having hens raise the little ones.
Some chicks learn a ramp within a few days, but it usually means the human has to be pro-active at helping them the first few days, they rarely figure it out without at least some amount of drama, and some broodies don't know what to do. Giving them an alternative safe spot at ground level in the run can help.
I would hate to separate a broody from her chick if that is the only problem....