An update on the perishable gift (which is not actually cake): I ended up leaving it on a neighbor's doorstep. I'm not close enough to her to feel yucky about my mom's gift in her house, but I like her enough to want her to have it. I was going to knock and tell her that I'd like her to have it, that for personal reasons, I cannot keep it, but she wasn't home. It was cold outside, cold enough not to worry about it spoiling, so I left it. I have no idea what happened to it, but I hope she assumed it was Christmas elves, and that she and her significant other have been enjoying it.
So, consistent with personal values, out of my house, not in a dear one's house. Perfecto!