I'm assuming that the shift lever is stuck in Park on cold mornings.

The dealer probably replaced the shift lock that prevents the car from being shifted without putting the foot on the brake first.

If that's the problem, it sounds as if there is some electrical fault having something to do with the overdrive switch. I'm not sure exactly what the problem would be, although it sounds as if there is either a ground fault somewhere in that system, or a bad connection (although they checked it).

She could just use the manual release on the shift lock, which is accessible by putting your finger in the hole where the shifter goes, at the back. There is a little yellow lever and you're supposed to pull it straight up. They are often broken, though, and I've seen several "conversions" where the shift lock setup was removed entirely, making it like a 1990 or earlier 240. That particular feature is a good safety measure but it can be pretty expensive and a hassle to fix sometimes.
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1992 940 wagon, low miles
as well as others.