Diana was an emotionally immature 19-year old when she got engaged and had just turned 20 when she married, and like young women of that age, probably thought love would conquer all and probably idealized and romanticized Charles rather than seeing him for who he really was. It is said that she did want to back out at the last minute but there was too much pressure on her to go forward with the wedding.
True. At her age, It’s hard to imagine the stress she was under. Especially since wasn’t very self-assured to start with.
IMO, she really had a raw deal in life.