Steph brought Spike to visit us today. Lucy came downstairs several times to check out the little intruder, and she didn't hiss at all. Spike barked at her once when she sniffed his rawhide bone, though. She's currently upstairs under the bed, and Spike is on the couch with me and Steph.
Spike will be staying with me later this week for a few days. He'll be restricted to the kitchen and back hallway when I'm not home, both to give Lucy some space of her own and to keep him out of trouble. He's been a very good guest so far this afternoon.