Will the Crazies Please Leave Me Alone

Many of you know our troubles with our not-to-be-named nanny that we had to fire when I was 36 weeks pregnant last October because she suddenly went from being the most wonderful person in the world to a raving lunatic almost over night. I recall the day in September when she showed up at our house in a not-very-friendly mood. Odd, I thought, but we're all entitled (some of us more than others) to off days. It was just a bit doubly-odd because over the course of the previous 14 months she hadn't had one off day, at least by my judgement. The following 4 weeks her mood only worsened, much to my frustration and exasperation. We had given her a week of paid vacation at the end of August so I was very puzzled by this - vacation leads to foul mood, hhhhmmmm. I tried everything I could think of over the course of September, eliciting the help of the other families in the nanny share who had also noticed a change in her moods. We tried talking to her, coming home early, buying craft supplies to entertain the kids, planning activities, etc. The big to-do was at the end of September when I showed up to pick up Graeme and the house was in chaos - VERY out of character - and she started ranting at me for overworking/underpaying her, and complaining that Graeme was uncontrollable and that she couldn't take it. I called time-out and set up a meeting with one of the other moms. We had a 2 hour discussion where she cried about missing her family, needing more money, feeling isolated, etc., etc. It ended with us giving her a raise and agreeing to try to communicate better. I was feeling pretty wiped out by the daily attempts to please her, but willing to do almost anything because of the amazing care she had provided over the previous year plus. That meeting was on a Friday and on the following Sunday the other mom called to basically say that psycho-nanny still wasn't happy and was probably going to look for another job. I decided I was done with the bullshit and fired her (with a voice mail message - how professional). I seethed about it, cried about it, and wondered what the f--- went wrong. Eventually, I just had to get over it though I admit to still harboring much anger. Well, yesterday I received a little thank-you note in the mail that said:

The MacGuire Family. It has been my greatest pleasure caring for your precious angel Graeme. I had lots of fun with him. Steve 7 Kelly (sic) I want to thank you for my W-2 form, your kind words and allowing me to work at your house. "Thank you." I did enjoyed working with you all with great respect and appreciation. Love Psycho Nanny (I made the last part up).

What the f----? Is this some passive aggressive move? A note written out of guilt? All it took was a W-2 form? Was I just in a late-pregnancy induced fog last October?

I seem to have developed a pattern of bringing out crazy behavior in other people, but this is really the cat's meow.