You’re in Canada? What type of bunny was this that you saw? Cottontails cannot breed with domestic (European) rabbits. They are a different Genus and the chromosomes don’t match up. Your rabbit should be spayed anyway though. At her age, she is at a greater risk for reproductive cancers.
You say you are keeping her outdoors? Why not bring her inside? It would be much safer for her and she would be happier. Is she unsupervised running around in the backyard? This is very dangerous because something see her as a prey item and snatch her. Any outside time should be supervised. As for the abscess, could she have been bitten and it became infected. Could the “dewlap” have been an infection, swelling, or fluid buildup? I wonder this since you said there is now an abscess there. Is there another vet that is closer? Even if they aren’t rabbit savvy, perhaps they could still assess the wound and consult the vet in Toronto over the phone.

It doesn’t sound like pregnancy at all – there wouldn’t be any lumps on the chest or neck area. I would definitely get her to a vet quickly. Abscesses can be common in rabbits and need a vet to treat

That’s true too. It is possible the abscess could be completely unrelated and it is a coincidence with the timing. It could be caused by a tooth or a number of other things.