She was born Maria Antoina Josefa Johanna and was married off at the age of 14 to a man she'd never met in a country she wasn't from. Her marriage was arranged to secure an alliance between Austria and France. She had to give up all rights to her Austrian heritage including her name.
She is most criticized for outrageous spending, ordering luxurious gowns and ostentatious wigs while France was suffering a financial crisis (possibly all the wars they'd been waging but who really knows) --but ironically also caused scandal because she eventually did away with big panniers and heavy makeup and preferred a more simplistic dress (The aristocratic were pissed because she wasn't dressed properly, and the peasant class was pissed because she was apparently role playing at peasantry-it became increasingly clear she had to walk a balanced line of public opinion).
And of course they hated her because she didn't get pregnant for several years. And when she did get pregnant they accused her of infidelity (nevermind that nearly every king, Duke, lord and what had a mistress, everyone knows its fine if men do it). Rumors about her flew because she was as easy to love as she was to hate and since she wasn't French and was often sympathic to Austria she was an easy target. She suffered several miscarriages and had two children die young. Some of the rumors about her are awful: that she wanted to bathe in blood of citizens or that she had an incestuous relationship with her son. Nevermind the "let them eat cake" thing. They made pamplettes (twitter hadn't been invented yet) to spread stories and rumors.
And then of course they killed her. By then the royalty already had no power. Keep in mind the revolutionaries who took over were not exactly "everyone gets the vote!" kind of guys. Napoleon would later crown himself Emperor even though he had partaken in the Revolution.
Marie Antoinette was, put simply, the Britney Spears of her time. Or Amanda Bynes or Amber Heard or even Hillary Clinton--or any woman in a highly visible, political environment atmosphere. She was a punching bag for France's frustrations. And long after her death the French have benefitted from her name and the imagery associated with her. They fucking love it; if the opening ceremony told us anything it told us the French love their fashion and scandal. Even in death she has become a mascot. La petite crucifixion or whatever.