I still have no idea what you are warning about. Please be specific about
what harm anyone can do to Judy by knowing both that unlock code and her
phone's IMEI number.

I think it is possible to track the phone's movements (provided
it's on) knowing the IMEI number. This works in two situations:
(1) you have a friend at the phone's cellular provider who has
access to cell phone tower data. However, if he's got
access to the tower data, he can probably do a phone-number-to-IMEI
lookup or customer-name-to-IMEI lookup just as easily.
and
(2) you are close enough to the phone to receive the signal directly,
with a "direction-finder" like device. Possibly it could
work better by pretending to be a cell phone tower and
getting the phone to respond to it. I don't know how common
these devices are, but I think law enforcement has them.

I think the unlock code is pretty useless, with or without the
IMEI number, unless you own the phone or plan to steal it.

Because some number is unique does not make it valuable
to anyone else who is seeking to do mischief.

A remotely readable unique number (e.g. cell phone IMEI numbers,
RFID tags (in, say, credit cards, clothes, etc.), toll tags, Bluetooth
MAC addresses, WiFi MAC addresses, etc. tend to be more abusable
in two ways: tracking/stalking someone, and spending their money.

The longer the range and the more related to money it is, the more
abusable it is. IMEI numbers are pretty long-range (I suspect
providers can do a network-wide international search, although the
radio signal probably reaches only a few nearby cell towers) for
tracking but don't seem to have much potential for financial abuse.
(At least on T-Mobile, the SIM card, not the IMEI, seems to provide
the billing info).

Credit cards with RFID chips may be readable for only a few feet,
making them not so good for location tracking, but the financial
abuse (and mistake) potential is enormous. I've witnessed two
people using Mobil SpeedPass accidentally pay for each other's gas,
then almost drive off before one of them noticed the problem (my
Toyota can't possibly hold 80 gallons of gas!).