My daughter said her 93 Nissan Sentra gear stick jumped from Drive into Neutral while making a loud noise. She was driving 25 mph. Could she have accidentally moved the gear stick without squeezing the button? Or could this mean transmission problems? Any ideas? She's scared to drive now.

Seatbelt or radio code?

it could be center bearing, if its going bad it can also cause a vibration, make sure you have sufficient fluid in the diff as well, you can also get a noise and vibration from collapsed motor or trans mounts

If noise comes from transmission in D range -no drive.Then i thing of AT internal problem. If in D during driving then you have to check drivetrain,like axles or bearings. or AT.

can you video it? could be many things could be a wheel bearing

SO take someone on a test drive and YOU can reproduce the noise for them. Maybe you have a transmission problem.

it actually sounds as if the high clutches in trans is slipping you have to have a pressure test done but be prepared to replace trans

Your noise sounds like it is power train related,If you have eliminated the engine,Since it doesn't make the noise while moving and in neutral.
It sounds like a universal joint in the drive shaft.Do you notice a vibration
along with the noise?

Sounds like a bad overdrive clutch, it's in the torque converter and is not repairable, you have to replace the torque converter, this is somewhat common on high mileage automatics, usualy it sticks locked, when you put it in gear it makes a clang and unlocks, but locks up as you drive and won't unlock when you slow down like it's supposed to

sounds like this one simply will not go into gear at all, either the clutch is worn out (They're vry small snd weak) or possibly a sticking valve body.

this needs to go to the dealership garage, NEVER go to Mr Transmission type places they'll want to overhaul it whatever's wrong, they don't waste time on diagnosis

You can try avoiding to place the car in PARK,when you stop the car just leave it in neutral and secure it with the handbrake.Inside the car under the gear stick should be a switch which suppose to keep the gearbox in park .When you push the break pedal it turns that switch on so you can place the car in to gear.Removing this switch can fix your problem ,but it is unsafe.The replacement of this part cant be too expensive.