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I would block the route up to the imac loft for now just in case. Can you get a biggish cardboard box and cut one end off then move the nesting material in there. Hopefully she will deliver in that if she is pregant and that will be best for the pups as you do not want them up in the attic in case they fall. It will also be hard to feed them up there. If she is not constantly up there in the nest then she is unlikely to have had them. You also see a large drop in weight at delivery. She may just be plumping up with all the good food. Our Allianna whi is expecting on Monday has gained 35g since mating, most in the last few days and she looks pear shaped and bulgy across the hips. If you feel the tummy it is firm and taught.
The wet spots on her hips are likely her scent glands especially if she is a bit warm in the attic or smells another hammy.
Try and get her moved on to one level. the weight you describe is not unduly large for a breeder ham (its middling I'd say) and we have had many this size and larger even from pet shops.