Hello there! I can tell you pretty much anything you'd like about Marie Antoinette's personality if you'd like to ask some more specific questions. Luckily we still possess a wealth of information about her from her own letters and accounts from her contemporaries.

As for the American Revolution, she was very much in support of it, though I doubt she understood the full complexity of the political implications of the war. Marie Antoinette was many things, but she was unfortunately not a very deep thinker on these sorts of subjects. She was a very genuinely good-natured person who was generous toward poor or unfortunates in a time when this was not a fashionable attitude. Her sensitive nature made her supportive of the revolutionaries simply because she viewed them as being an oppressed people who were deserving of justice. Also, as the French Queen, she was probably in favor of any actions that would harm England politically, as it was one of their main rivals for power.

While Marie Antoinette did not wield much political power in her role as Queen, she did have the ability to be a sort of patron to certain persons. She campaigned behind the scenes for a number of years to get her close friend (and possible lover) Count Ferson a place in the American military. Many French and other foreign men were intrigued by the prospect of glory and possible riches to be made during the war, and they were excited to fight the British. Even before the King agreed to send troops, many independently financial men went to America to fight anyway, most notably Lafayette.

If you give me some time I may be able to come up with some actual quotes by her about this subject. You will be surprised to find, though, that Marie Antoinette was a generally innocent woman who was very sweet and passionately adored by her servants and most people who met her. While there have been many Queens in history who have deserved a terrible reputation, Marie Antoinette was exactly the opposite of how she was viewed by the revolutionaries. If they had each been able to meet her and known her true personality and intentions, I believe they would have embraced her as their Queen. It has been noted several times, even by people who despised the Queen for political reasons, that they still could not be unaffected by her charm and sweetness.

edit: I realize now that I've written a lot in this thread and haven't given any sources. Most of the facts and stories in my replies can be sourced to the most complete and well-researched book I believe to have been written about the Queen: "Marie Antoinette, The Journey", and I highly suggest anyone interested in her to give it a read.