So, here is the new plan. YAY!
I am going to purchase something called Feliway, a pheromone that seems to really calm cats down, especially in multi-cat households. The cat lady just introduced it into her home this past weekend and she said the change is amazing. I plan on using the diffuser in both rooms.
So. Feliway for a couple of days, litter box under the buffet in the outer room in addition to the one in the bathroom (two totally separate spaces), and we’re going to try one more time. If there are separate litter boxes and Miss Mitty doesn’t have to go through JL’s territory and there is something that calms them both down, then perhaps this might work.
I will pick JL up again on Saturday morning.
An aside, when I run the vacuum both JL and Miss Mitty hide under the bed with no hissing or anything. Me and the cat lady laughed thinking about the vacuum being our training tool. Just kidding! but the common enemy does seem to force them to set aside their differences.