It's ok to take the eggs away (both real and plastic) and keep removing her from the nest and denying her access to it, but I have found that once they really settle into going broody there is only one reliable way to get her out of it - a broody buster cage.
I know it sounds cruel, and I was always vehemently against it - until I had a girl that just sat and sat and sat. It was hard on both of us, but by far the better alternative to letting her starve, sitting there on her empty nest.
I would recommend you get yourself a good dog or rabbit cage with a fine wire base to it. Position it so that it gets a decent breeze under it! Put it up onto blocks so the air can flow freely underneath it, and put in a water bowl and a feeder, but no bedding. Make sure the cage is protected from the elements - so a roof over it (a sheet of tin will do) if it's raining or hot out, and protection on the sides from the wind if it's really cold.
Then put her into the cage and leave her there for 48 hours. Don't worry about her being lonely - if she is truly broody she will want to be 'alone' anyway. She might pace back and forth for an hour or so, and may even squawk a little bit, but I promise you she will settle down and accept the cage. You just need to walk away and let her be for a bit. After 48 hours take her out and let her stretch her legs, but if she so much as looks in the direction of her nest - back into the cage she goes.
My girl was super-broody! I used the cage in heat of 100F over Spring, so it took a little longer than it normally would to cool her down! All up she was in there for about 6 days, and after the first 4 she would go out free-ranging for a few hours before heading back to the nest. That's how I knew it was working.
After 6 days in there she went back to normal. Happy, healthy hen. She started laying within a couple of days after that.
Honestly, it was so much better than leaving her in the nest with no hopes of hatching chicks.
Good luck to you!
- Krista