Great timing - my Light Sussex (Suzie) has just gone broody as well. She does so every three months or so. Not a huge problem, as there is room in the nest box for the others to lay - but obviously she stops laying, and she's usually my best.
A long time ago I read on another forum that you need to cool them down to stop them being broody. Just leaving Suzie to it doesn't work, she'll just keep sitting if I let her.
You definately need to separate her. I've read up a lot of advice on this, and this is what I do:
1. Section off a part of the run to create a separate broody pen. Has to be secure. Needs shade during the day, don't do it in the rain
2. Within pen, put a mesh floor on to raised blocks. I use wood, about 2 inches high
3. Ensure that you put in a water & food supply
4. Leave the hen in for 3 days & 3 nights
The theory is, that alowing cool air to pass under the hen, it cools them down and stops them being broody.
They'll then start to re-grow the feathers that they've pulled out to allow skin-to-egg contact.
I've successfully used this approach a few times.
The hardest part is knowing that the hen is in the cold at night - but I believe that this is the best way to cool them down, and stop them being broody.
A friend-of-a-friend is apparently talking about culling a hen who keeps going broody, which is way too extreme...
As the weather at the moment is relatively warm at night (forecast to be 14, 12, 12 degrees here for the next 3 days), it's a good time to do it.
Hope that helps.
