1995 Audi A6 Quattro 140,000 miles

1995 Audi A6 Automatic Quattro 140,000 miles

My sister drove home and as she was getting close smoke started to pour from under the engine bay, my Dad determined it to be transmission fluid leaking. Filled the fluid up and now the car will drive forward but not backwards. we plan to replace the Gasket on the pan as it looks to be leaking there. any ideas what damage may have been done? or what to look for? when the car is in reverse it will rev freely as though the gears are not engaged at all. this is a bit of a pain as my Dad replaced the timing belt and water pump a couple days ago.