When you say annual feed, you don't mean you only feed them once a year do you?
Anyway, as to laying... I would NOT recommend a laying box unless you don't have any other choice (like they live in an aquarium or something) because they will not enjoy going to a small box and will stress and likely not lay. My gals held their eggs last year and all only dropped very reluctantly and I had horrible hatch rates for the year. I used the bins because I had no choice, I had just bought my house and moved and had no fenced yard yet to build the pens in... so...
You could partition off part of the pen, but I bet you could just check on her as often as possible. I'd recommend having a mound of dirt with some sand mixxed in. It doesn't have to be too large, but sometimes they like to get above the normal ground level to lay their eggs. You can mound up some dirt, mix in sand, tamp it down really firmly, then put on some grass seed and water it and then leave it alone. Then it will just be a grassy hump eventually and won't look odd in your pen.
If you catch her laying, which you probably will if you check every night, don't disturb her. Put some rocks or sticks on the outside of the pen on two sides that if you imagined lines from them through the pen they would cross where she is nesting. Then give her the space she needs (especially important not to disturb her at all while she's just digging, after she starts laying you can watch and snap some photos, they seem kinda zoned out then). Often they go LATE into the night with the nesting so you can check the spot the next day and carefully transfer the eggs. If she finishes before it's too late and starts filling it in, let her finish up and walk away before raiding the nest (common courtesy *grin*).