I’m more familiar with these types of tickets than I want to be, so here goes:
First, review the ticket you got in the mail very carefully. I have no idea where you live, but rolling through a stop sign may be a general, not personal traffic offense when it’s enforced with a camera. In other words, like a parking ticket, the ticket belongs to the car, and therefore belongs to the owner of the car, whether the owner was driving the car that day or not. In my jurisdiction, when a camera is used it’s not longer a points-eligible offense, which is how they get around who is driving. Again, the ticket belongs to the car and the car’s owner, just like a parking ticket. If you lend your neighbor your car and he gets a parking ticket, to whom is it issued(and who has to pay)? This obviously depends on the operative statute in the locality where the ticket was issued.
Second, if you are a co-owner, under the parking ticket theory, you could well be liable. My guess is your wife was the first listed owner, which is why the ticket only came in her name, but if you are the co-owner of a vehicle with a deceased and now previous co-owner, how was the car originally titled? Did ownership of the car, by operation of law, pass to you automatically upon her passing?
Third, you may want to see what if any obligation you had to re-title the car under state law after your wife’s passing.
And again, it may be just like a parking ticket. Lots of folks ignore those and have no problems. My luck is such if I were to ignore it, I’d get booted.
Anyway, you can see a lawyer($$$) or do a quick internet search of your state law. But it seems as if you have a very good idea who was driving the car on the date in question, so have them pay.