Are you sure the transmission is shifting to1st gear and not 2nd?  The
transmission computer is designed to go automatically into "limp home" mode
if it detects and error from any of its sensors.  Limp mode is 2nd gear.

I'd take it to a competent transmission service shop that has experience
working on Chrysler transmissions and get the codes read.  It could be
something simple, like a vehicle speed sensor, which has failed so needs to
be replaced.

These transmissions are also extremely sensitive to the ATF fluid type. Make
sure that it is full and only use ATF+3 or ATF+4 - nothing else.  Also make
sure the trans shop uses this as well since many will try to substitute GM
Dexron and this will appear to work OK for them but will certainly kill the
trans over time.

Also, tell her that trans needs regular maintenance as well.  The pan should
be dropped and cleaned and the filter and fluid replaced with genuine
Chrysler about every 30K miles.  Also, there is a differential gearbox up
there in that trans axle too.  It should be flushed and refilled per the
maintenance schedule as well every so often (I did mine at 60K miles when I
was doing the trans fluid and filter).

Let us know what they find.  I have a 1996 Eagle Vision TSI (same as the
Intrepid) and a 2001 Intrepid that both have that transmission.

     Bob