im new to this site so i hope i put this in the right place...and i dont exactly speak the "car language" perfectly and i may sound like a total dumb girl but im going to try my best. ive been on google all day trying to find answers and stumbled upon this site so im hoping someone can help...

i have a 2003 audi a4 3.0 its an automatic. i got it used from a dealership about 2 1/2 years ago, i got it at the end of 2009. its always driven awesome, no serious issues or anything. well, this morning i left the house, made it to the highway and had to stop to wait to pull out, and then when i tried to go, the car wouldnt move it just rolled out onto the road (and was still running). so yeah, it was quite the experience in traffic. i had to have the car towed back to the house because i couldnt get it to move. they told me its the transmission and started rattling off the costs and how they could fix it and its obviously not cheap. i was just wondering if anybody had any other ideas of why it would do this? does it sound as though its definitely the transmission? because the car never showed any signs of transmission problems, ive never noticed a leak, its never slipped or surged while driving, it always picks up and goes no problem and shifted awesome. i tried to check the transmission fluid but i noticed theres no dip stick for it so im assuming i have to get under the car?

thanks for taking the time to read