Clutch Pedal Vibrations

My clutch was fine yesterday (aside from the squeaky TOB that needs replaced) and today my mom needed to pick up her vehicle from the shop so I had to go with. She wanted to drive so I let her. She usually drive an auto and doesn't like driving a manual much but I watched her drive and it was terrible. When she had to slow down to 15-20mph from 35-40 she wouldn't downshift to first (or even second). She would just give it way more gas and slowly get back up to speed. When she did shift she revved it up quite a bit as she let out the clutch (yep, my mom kinda power shifts). So we got to the shop and she got the keys to her car and I started mine up and as I started going I noticed the clutch pedal was vibrating a lot. I had the music cranked way up and I turned it off to be sure it wasn't just the car vibrating from the speakers but it kept vibrating a ton. I've driven the car a bit since earlier and it's settled down some but it's still vibrating more than it would be with just the normal vibrations of the vehicle.

So what generally causes the clutch pedal to vibrate? I'm going to have to teach my mom how to drive better, but would her power shifting contribute to the vibrating clutch pedal?