Hi! Welcome to BYC! I have the occasional egg on the ground too. I just pick it up. It's not often, and I don't even know if it's the same hen. You might try putting her in the nest box, if it's the same girl all the time. Put a ceramic egg in there. When she lays on the ground is it in the open or in a dark corner? A dark corner would indicate she wants more privacy, so maybe curtains on the nest boxes. How many chickens do you have and how many nest boxes?
How many nesting boxes do you have? Has she ever laid in a nesting box? If not, lay some fake eggs or golf balls in them so she learns where she needs to lay. It’s not uncommon for hens to lay outside of the boxes, especially if there are lots of hens wanting to lay at the same time. Good luck!
Is your hen truly laying on the floor, or is the egg perhaps falling from the nesting box onto the floor? That is possible. It happens in my flock. They like to lay in the same box and after about 7 eggs, one will roll over onto the floor. Most of the time it's not broken either! If she is laying on the floor, it's for a reason. The other hens don't let her in the box, or it's too dark and she can't really see to find the box (some hens lay very, very early in the morning before the sun is up, one of mine does that). I have night lites in the coop for that reason, now just that bit of light allows her to see and lay in the box.