There are a lot of things that have to happen in order for a snake to become gravid. Frankly, if they were only "locked up" for a short period of time, I don't think you have anything to worry about, and here are the reasons why.
My first question to you is, JUST IN CASE your female did become fertilized, what is her weight? Do you have a way to weigh her? I am curious because it's important to breed snakes when they are at the correct weight and age, and she is just barely at a breedable age, so it'd be important to know her weight.
When cornsnakes are readied to be bred in cap, they are brumated for 6-8 weeks at a time. This allows them to basically, get ready, for mating. This is a bit of info from a cornsnake breeder;
"While this brumation all seems boring, it provides a bit of rest to the breeder, and more importantly to the snakes. Remember that egg follicles are developing and spermatogenesis is occurring in the males as well. It's important to maintain good conditions during this time so that all goes smoothly or infertile eggs will surely be the result. We also use this time to select which males will be placed with which females to produce the desired offspring. While some will breed earlier, we prefer to breed males beginning at age two, and females at age three."
Brumation readies the snake's body to go through the mating process. It's seen as a resting time. It also entices the snake TO mate. Technically, a corn snake does NOT have to be brumated to successfully mate, but brumation does increase the chances of successful mating.
With that being said, there's a very good chance your female doesn't have any follicles at the current time. It is also possible that your male isn't quite ready for breeding, 1 1/2 yrs old is a little young to be breeding a male corn. (I do understand that it was not your intention to do so, so don't get me wrong, I'm not yellin' at you for it, haha). Most often, it takes multiple copulation attempts for the egg follicles to be fertilized. But, there is the off chance that she did become gravid.
In the case that for whatever reason that she did, you will begin to notice abdominal swelling, and at this point a veterinarian or someone with the knowledge of breeding can feel her to see if she has follicles that are becoming eggs. If this is true, you will want to feed her frequently so that when she delivers her eggs, she is strong and does not lose a substantial amount of weight.
The female will lay her eggs around 25-30 days after copulation, sometimes a few days sooner or later depending on the female. About 1-2 weeks before she lays, she will shed, and after this shed, she will not eat. Don't be alarmed by that, she just knows that she can't have food processing in her tummy when she goes to lay eggs.
When you see her pre-lay shed, that is when you should prepare the nest box or "lay" box. Typically, plastic storage boxes are the easiest way to go about doing this. Fill the container half full with either sphagnum moss, or vermiculite. The most common is vermiculite, which you can find at a typical hardware store. It should be slightly moist, but not dripping wet. This helps keep the eggs from dehydrating. Don't disturb her while she is laying, let her finish completely and then give her a few hours to rest. Always offer a -small- meal after laying, so she can get some nutrients into her body. You may have to remove her from the lay box as well, and there's a chance she may be defensive when you do so, so just be respectful of her and remove her to a different place.
Now, incubation is the hardest part of the process. Temperature and humidity are key to successful breeding. With improper temps and humidity, you could lose your entire clutch, or birth defects can be caused, such as domed heads, kinked tails, etc. You can use a hovabator, which is an incubator designed for reptile egg hatching, or even a poultry incubator. If you don't have one, or don't want to buy one, there are TONS of videos on youtube on how to make a homemade incubator using a styrofoam cooler, heat tape, and a thermostat. Ventilation is important, so make sure you have holes around the top if you use the styrofoam method. For cornsnakes, incubation temp must stay between 80-85, with an ideal temp right around 82, preferably. NEVER any higher or lower than that. Using a 1:1 ratio of vermiculite to perlite is the best medium for the incubator. Keep it most, but never too moist, if you can wring water out of the medium, there's too much water. Place the eggs into the incubator, burying them 1/2 way down, so the top half is still visible. Give 1-2 inches of space between eggs, if space allows, otherwise make sure there is at least 1/2 inch. Typically, the snakes will hatch after 50-60 days.
When the snakes hatch, let them stay in the incubator until their first shed, which is normally right around a week after hatching. At this point, they can be moved into their own tubs. You can then offer them their first meal, always use day old mice pinks at this point. :)
PHEW. Hope that helps, I figured I'd get it all out in one go.
If anyone has any other tips, or wants to correct me on anything, they are more than welcome to, this is not an all inclusive guide, haha. Just what I've seen and done that works. :)
Good luck with your gal. Sorry i wrote so much, but I hope it helps.