Thanks to all of you
We decided to keep the pet stairs up last night and not allow them onto the bed for a while. Luna cried for a while, but I got up to use the bathroom, and when I was getting back into bed told her "go to your bed". She did and I actually got the best night's sleep I've had in a long time.
It's so weird that this only happened in the middle of the night, leaving me to wonder if Luna was just so deeply asleep that Izzy scared her really badly. Izzy tends to start out in her bed beside ours, then I think she gets cold or lonely and creeps up to Daddy in the night.
Oh well, problem solved, at least for now! We're working on reminding Miss Luna that she is NOT leader of the pack
