Odd that an ISA would take break so soon.
Was there any other changes in flock or coop when she stopped laying?
Are eggs on roost hard shelled or soft?
What all and how exactly are you feeding?
Is your coop crowded?
Dimensions and pics of coop, inside and out, would help...
.... with number, ages, and genders of birds.
The coop and run are a little small, it was planned for 3 birds but we brought home 4. The coop itself is 4 feet by 3 3/4 feet, 15 sq ft plus 2 external nesting boxes. There is a waterer in there but no food (that may change now that it's getting colder). There is a single roost, about 43" long and a foot or so high across the center, there is a tray of sand on the floor under it for easy scooping.
The run is also small, 8 1/2' x 3 3/4' or about 35 sq ft. I'd hoped to let them free range occasionally but it hasn't worked out. Food, water and oyster shell available in the run.
We have 4 pullets, 3 hatched around 5/1 and one is about a week older. They all came home on 5/5. Aside from the ISA, we have a RIR, a Black Star and a white Leghorn. They went from starter to flock raiser crumble in late August (plus oyster shell and grit). The ISA laid first, around 9/10, the Leghorn started about a week later. Both had the same pattern, first egg, a day off, 5 to 7 more normal eggs followed by a shell-less egg or two and then a couple weeks off before starting up again. I decided to switch them to Layena (the new "free range"s variety ) as a precaution after the shell-less eggs. The RIR started laying about a week after the Leghorn and also took a day off after her first egg, but she went non-stop for 2 weeks before missing another day. The Black Star, the oldest bird, didn't start laying until early October but has been somewhat consistent since then.
The ISA, as mentioned above, layed about 8 normal eggs in about 9 days before laying an egg with no shell at all. A few days later there was another egg with no shell but we don't know who did it, she took about 3 weeks off before resuming and was in the nesting box every morning around 10 for about 2 weeks before missing another day. In the 3 weeks since then we've found about a dozen eggs in the poop tray before sunrise, one egg that was in the nesting box before sunrise ( and her on the floor, next to the box) and she's skipped a few days as well.