Why are my dogs eyes swollen?

definitely sounds like an allergic reaction and you said since the weather has been cold you have had your dog in most of the time except for when she goes to the bathroom and is supervised. then it is definitely coming from the inside of your house and there are many things that a person doesnt even consider that a dog can get into and have an allergic reaction or even some house plants are poisonous. maybe she has been a little more bored then usual because of the weather i know mine have been and possibly she got into something that you havent noticed, like a plant or something of that sort. just an idea anyway. hope you find out what it is that she is allergic too and i hope the best for you and your pup.