How long has your hen been broody? I always wait until they've been on the nest 2 nights in a row before I give them the eggs I want to hatch. If they don't spend that much time on the nest, they're not truly broody yet--I've had too many flirt with broodiness for up to 2 weeks before they actually settle down to it. Once the spend a few nights on the nest, IME they're in it for the long haul.
So, if you're thinking she's just now broody, you have a few days to collect fresh eggs to put under hen. A full size hen can easily fit at least 6 large fowl eggs, even if they're XL size. You can sure put fewer if you're more comfortable doing that.
When I have a bird that's acting broody, I hold out the eggs I'll want to incubate so I have a good clutch when I'm ready to set them. If you don't have all the eggs you want to put under her, you can wait another day or so--I wouldn't go much past 5 days or she'll be more likely to quit on you just before hatching.
