Well.  It turns out I should've just been reasoning with her this whole time.

Last night woke up one time, when her Benadryl wore off.  (No, Internet, I don't drug her to sleep - she has a very runny nose due to a cold.)  I gave her some more, then rubbed her back for a while.  I thought maybe she was faking sleep, but I decided to take a chance as I backed out the door.

Little angel:  "MOOOMMMMYYY!!"

Me:  (re-enter room)  "Okay, angel, it's like this:  Mama is tired, too.  I need you to lay down here with Gray Kitty and Orange Fishy and go back to sleep. It's sleepy time.  Night-night."

Leave room.  Angel calls out to me, my beloved and Jesus for five minutes.

I go back in.  I try a new method.  I squat down and look her right in her blue, blue eyes.  She has big, fat crocodile tears on her cheeks. This makes is difficult to be firm, so I wipe them off.  She nuzzles my hand.  Ah, this is difficult.  I just want to snatch her up and take her back to bed with me so that I can sleep, too. With my beloved gone, I have been spending too much time thinking about the break-ins that happened down the street not so long ago.  I wipe her nose with a tissue.  She smiles.

Me: "Okay, angel.  Do you see Mama's door? "  I point dramatically at her door, through which you can see mine, mere steps away.  They are actually perpindicular to each other and I can stand with one foot in each room, if I want to.  "That is where Mama sleeps.  I can hear you perfectly, so you don't have to cry. I can hear every little sniffle.  I will come in if there is something very wrong, so you don't need to worry.  Now go to sleep."

She looked at me dubiously, then laid down, picked up Gray Kitty, and closed her eyes.  When I left, she cried for exactly one minute.

I was so surprised, it shocked me wide awake.  Took me an hour to get back to sleep.  I guess next time, I'll just go straight to logic.