Normally, if a female was lactating (without having a litter of pups) -and feeling ill as well, with a fever, I would immediately suspect Pyometra.
Pyometra is an infection of the uterus, where the uterus fills with pus, and needs urgent attention, usually surgery (hysterectomy) and intravenous fluids. It comes on usually a few weeks after the "heat" cycle (though it CAN happen any time, and can even happen DURING the "heat" cycle) -though about 8 weeks or so after is far more common.
Usually that is around the time a "False Pregnancy" will occur in dogs susceptible to this hormonal imbalance. So that is what would make me suspect it.
However, I can't see the relation to a swelling on one side of her throat -so the false pregnancy symptoms could just be co-incidental.
It does sound more like a reaction maybe to a sting or bite. I don't know what insects etc could bite at this time of year. It is possible for bees to be around if the weather is mild. It's also possible that a stray bee could have got inside your house during the Autumn, and survived....(?) Bit of a long-shot, but possible.
Another idea if swelling of the lymph node in the neck, possibly as a result of some localized infection-source, such as an infected back tooth, probably lower-jaw? Did the vet check this? That could also cause a fever in some cases.