I am in need of some advice. Today I found my AWOL Orpie hen, brooding on 18 eggs in the middle of a mesquite bush. I know they're not all hers...3 of my other hens have been contributing, so I have no idea if some were laid there after Princess started setting (meaning staggered hatch dates

). How many eggs can one hen successfully keep warm?
She had a nice hollowed out nest in the ground, and had all 18 covered. They were all equally warm when we took them out. But in the broody pen, she just has hay in the bottom of a pet crate now, which means it's harder for her to get them all covered. Should I take some eggs away in hopes she can hatch a smaller number? Or just let her have them all since it's already been almost a week, and I have NO idea if they're all in the same time frame, or which ones would be viable or not?
I have no way to candle, and I'm leaving on vacation tomorrow, so I will have to either take some away tomorrow morning, or just leave them all be. I don't want to break her brood, and I don't have any fresh hatching eggs to give her, either. :/
What should I do?