First, try to bracket the problem. Isolate the problem to either the pedal assy, throttle cable, or throttle assy. Cables can get kinked inside the sleeves by abusive repairs. Also look for interference and weak or broken return springs.
Definitely get to the bottom of this problem. It's a serious safety issue. In the meantime, make sure your daughter is trained to properly deal with this problem should it happen again, such as shifting to neutral and turning the ignition key to the OFF - but not LOCK - position, so she can turn off the engine yet still steer.
95 E320 Cabriolet, 131K