As Egghead said, mark the 5, check every day and remove the rest. If she abandons the other three eggs after the first ones hatch, you can either try to incubate the others, or just toss them. Or, ,maybe you can candle them and get rid of the ones that are less developed than the others, if they're obviously way behind.
For future reference, next time you get a broody, collect eggs for a couple of days, remove what she's sitting on and give her marked eggs. Easier to remove extras that way. I draw a circle around mine so I can see at a glance no matter what position they're in that they belong there.
Depending on the size of bird and the size of the eggs, a broody can cover up to a dozen, sometimes more, eggs. The reason the other hens lay in the broody nest is that chickens just like to lay eggs where someone else is already laying. Maybe they figure, "Hey, if she's laying her eggs there, it must be safe since the eggs are still there. No one has found and taken them yet!"