Agree with cigroller. The only time I had a need to warm up my transmission was in the North at -35 when I had to park outside. The engine would start, but the transmision would not shift into gear untill after about 10 minutes. This was on a 2 wear old 1977 Pontiac Lemans.
Your woman friend needs to have her transmission fixed before it fails altogether. You can’t put a block heater on a transmission, but you can use a magnetic clamp-on heater for a short period. That won’t solve her problem though.