Pretty sure I've read they drop off slowly, over a few years, not go from 3 to 5 eggs a week to nothing all of a sudden, though I could be wrong. I read a chart (which I tried to find later and couldn't) showing laying over the life of a hen. At 5 years, they tend to lay about 50% of peak. So, if a hen was laying 6 eggs per week at 15 months, they should still be laying 3ish eggs at 5 years old.
Now, how this might be affected by breeding that increases laying early, I have no idea. But to me, it sounds like something (heat maybe?) stressed her out, and she's stopped laying temporarily.
