Re: 4 y old get out of car seat
What kind of seat is she in? Is it a booster seat that just positions the car's seatbelt across her or is it a seat with a harness in the front? Have you had the seat for long?
If you haven't had the seat long maybe you should take it back to the store and explain the issue you are having. Perhaps they will let you swap it for one that is harder for her to get out of. I know some stores have display models and with thier permission you can try seating her in them and getting a feel for what her little fingers can do.
My sister has the same problem with my neice. She finally found one that buckles between her legs and then across her chest. She can't press the button between her legs because of it's position so now she is unable to get out.
Good luck to you!