How many days in a row has she not laid, “last week” is kind of nebulous?
A very common cause for chickens to stop laying all of a sudden, other than the molt, is that they are hiding a nest on you. They haven’t stopped, they just change where they are laying.
It’s possible something could be getting the eggs. A lot of critters generally leave evidence nearby if they eat eggs, actually how they eat them and what they leave behind can be a clue as to what is eating them. The common critters I know that usually leave no evidence behind are snakes, canines, and humans, but not all critters of a certain species always does what they normally do. Some of them can surprise you.
Some hens and pullets reduce or even stop laying in severe weather, hot or cold. I agree 40 is not a severe cold, but chickens often do not handle change very well, it could be a large change in temperature. That’s why Aart asked about changes. The more information we can get, the better out guesses as to possible causes can be.
I’ll expand a bit on Aart’s list. Have you changed where she is housed or made changes to where she spends her day and night? Has she seen any lighting changes? That could be a new light that makes her day longer or maybe a security light burned out so her day is shorter. Have you added or taken away any chickens so the pecking order is upset? Are there pecking order issues, different flock members mature at different rates so the pecking order can be disrupted as they make their way into it? Did she go a spell without water? Has someone started building a new house next door so the noise frightens her? What has changed?
Is she broody? Broody hens stop laying.
Have you checked her for mites or lice? Since she is acting healthy it’s probably not worms. An overload of parasites can stress them and cause them to stop laying.
Then there is Yorkshire’s point. Sometimes a hen, often a pullet, just stops for a while for no apparent reason.
Look for behavioral changes and check her out for parasites. Other than that, patience is probably your best friend.
Good luck!