Of course it's when you
want them to stay broody that any little disturbance can break them... as opposed to when you are actually trying to break them, seems like no amount of moving or jailing can snap them out of it
So I wouldn't risk moving her, if you want her to stay broody. The whole thing is just too fickle. Blocking the nest off to keep the chicks in is a good idea, but then the hen won't be able to go eat and drink. Unless the nest is big enough to fit food and water? Or if there's an adjacent nest and you can take out the divider between the two, to make the space bigger and then put food and water in there? If you only have two nests (like I do), you can make a temporary nest out of something else (milk crate, cardboard box, etc) for the other hens to use, while the broody is occupying the other nests.
Or, alternatively, you can make a ramp for the chicks. A multi-level ramp can give you gentler slopes than a straight-down ramp would. My nest box isn't very high off the ground, but I made a two-level ramp just to make sure the chicks could get down. Here's what it looked like:
View attachment 2702081
The chicken wire is where I divided the coop in two to keep the other hens away from the broody. I only did this after lockdown, so they wouldn't trample the chicks as they were hatching. My hens nest-share sometimes, and the others kept laying in her box as she was sitting, so I didn't want them doing that while chicks were actively hatching. When all the chicks had hatched and the broody had led them out of the box, I removed the divider and let her introduce them to the flock.
Don't make my mistake and use chicken wire for any kind of dividers though! I discovered the hard way that young chicks fit right through the holes. One of the broody's chicks slipped through but couldn't figure out how to get back, and was stranded without her mom on a 40-degree night. I discovered her accidentally when doing a late night check up, and put her back under her mom, but that would've ended tragically otherwise.
If you don't have enough room for a multi-level ramp, you could also make steps out of bricks, blocks or stumps, leading down from the nest. Little chicks can't jump up very high, but they can jump down much better. All they need is to get down, and once they're all down, you can remove the ramp/steps and give them a different nest or box to sleep in at ground level. They may or may not use it though. I left my ramp up and the chicks were capable of using it, and I also left a ground-level box with bedding in it. However, the broody liked neither, and slept on the floor of the coop instead, with the chicks under her.