Toddler getting out of car seat

My daughter turned 2 in February. Her old car seat she learned how to unbuckle the top part, and we thought switching car seats would help. Plus hers needed replaced anyways. We bought a new one and all was good for 2 months. Now, she has started unbuckling the top part again. I guess she learned how to do it by watching us take her in and out all the time and figured it doesn’t take much to get it undone. She hasn’t figured out the part that goes in between her legs yet but she was trying.

How can I stop this? I have told her no a thousand times. It scares me because I can’t constantly watch her while driving and she does it so quietly.