Cedar is not necessarily the reason it was sneezing, just to let you know. Many rabbits are fine with both cedar and pine bedding, some aren't.
As for the sneezing, is there any discharge? Generally infectious snuffles (snuffles is just a catch-all phrase for anything that causes sneezing, discharge, etc. which can include allergies) include white or coloured discharge whereas allergies or stress can cause clear discharge. If it is coloured or white, your rabbit probably has pastuerella, staph, bordatella, or one of the less common bacteria that can invade a rabbit's system. If it is clear, she might just be reacting to the stress of the cold. Getting a culture done at a vet's would be the best option because then you can see exactly what is going on. You can tell if there is actually a bacteria in the nasal passage or if there is nothing to be alarmed at.
Definitely keep it away from other rabbits, because if it is one of the above-mentioned bacteria it is extremelly contagious.
As for the breeder, it may not have come from the breeder of that rabbit. The petstore may have gotten rabbits from different sources (or from a dealer who buys from several different breeders) and the rabbit got ill from a different rabbit. It is not really true that they usually get it from their mom. Sometimes the babies actually have a higher immunity to the disease if their mother has it (We found this out when we had a pregnant doe get bordatella. At that point we could do nothing; she was already pregnant. Turns out the babies were all fine, and they were some of the few in that section of the barn that did not get bordatella.) They usually get it from a rabbit near them. Pastuerella (generally thought of as the most common bacteria to cause snuffles) can travel clear across the room from a sneeze and infect a rabbit all the way on the other side of a room. Obviously, the closer a rabbit is to an infected rabbit and the longer it is by that rabbit, the more likely it is to get sick as well, but the bacteria is extremelly infectious. It can be carried on hands and clothings, on rabbit equipment, etc. Some even theorize that it can be carried in the lungs of people who visit a barn with infected rabbits, especially if there are a lot of infected rabbits.