Just a quick update. The pretend wailing happens less, thankfully, but it occurs now more in boredom and drowsiness, I think. She'll alert me to something - usually stupid - like her shoes being upside down in the hall, and whilst she's not at all upset about it, she just wails slightly. She's not crying, and she's not pretending to, she's just taken to making this noise.
She lays on her bed sucking her snuggle blanket and wails.
She does it usually in laughter, almost like a nervous laugh. Yesterday her daddy pretended he forgot where we lived and drove past our house, and she giggles and wails at the same time.
It's an awful awful awful sound but honestly I'm just truly glad it's not actual upset whinging.