Car Revs But Won't Move Forward

Today my daughter was having trouble getting her car to move forward. She would press on the gas and it took seconds to engage. It would then go forward until she stopped and had to engage again. This went on as she attempted to get home. Finally, it stopped going forward at all. When in park it won't roll. She had it towed to a shop and when she started it again she was able to get it to move forward but then when she tried a second time it wouldn't go forward again. Thoughts? We're having it looked at on Monday but trying to prepare myself if it sounds like a new transmission is needed.