If she spends the nights on the nest instead of roosting in her normal place, she is broody. If she does not spend the night on the nest, she is just teasing you. You'd be surprised how many do that.
Cochin come in all sizes, from bantam to full-sized. Eggs come in all sizes. If the hen can comfortably cover them, she can hatch them and raise the chicks. For full sized hens I usually go with about 12 eggs laid by full sized hens. Some bantams would struggle to cover four full-sized hen eggs.
Sounds like this hen needs to be locked up where she cannnot get confused. I'd guess either she is real easily confused or maybe another hen is on her nest when she gets back from her daily constitutional so she just takes another nest. If you can, I suggest you fix a place that has one nest and room for feed water and for her to go poo, then lock her in there. Don't let her out and don't let the othe chickens in with her. Many hens can successfully hatch eggs while they are with the flock, but some can't.