Marie-Antoinette was very popular more or less up until she became Queen in 1774.

The marriage between the Dauphin Louis, soon to become Louis XVI, and Marie-Antoinette was meant to consolidate the alliance between France and Austria was welcomed by the people as a promise of continued peace, if not as a coming golden age.

As soon as Marie-Antoinette set foot on French soil in 1770 she made all the right PR moves. For example she asked the mayor of Strasbourg who was complimenting her in German to speak French to her, as as of this day she wouldn't know any other language. At every stop along the way to Paris, she appeared smiling and was gracious to everyone.

By 1774, Marie-Antoinette already had serious political and personal enemies within the court, she was apparently unable to produce an heir, and the first vicious pamphlets started appearing.

If you can read French, I would recommend these two books which describe the beginnings of Marie-Antoinette in France very well:

Marie-Thérèse et Marie-Antoinette by Marie-Célestine-Amélie de Ségur d'Armaillé
Marie-Antoinette, les dangereuses liaisons de la reine by Michel de Decker

You can check this book online about public opinion in the 18th century based on correspondence and memoirs:
L'Esprit public au XVIIIe siècle by Charles Aubertin

You can also take a look at the political and obscene pamphlets against Marie Antoinette, it's interesting as well as good fun:

Marie-Antoinette libertine and Les pamphlets libertins contre Marie-Antoinette by Hector Fleischmann

This is a great question! I understand your confusion, because the popular image of Marie Antoinette is fairly negative (and the popular image of the Revolution is that it was inevitable, due in large part to her personality flaws).

(Sorry this took so long. One of those days where you keep getting called away ...)

The main problem that Marie Antoinette faced on arriving in France as the proxy-married wife of the dauphin was that she was there as a representative of Austria, and Austria and France had been enemies for generations. Someone else would be better to explain the details of the rivalry, but by the early eighteenth century it had become a tautological loop of "we hate them because we hate them". However, the two teamed up against Britain (and lost) in the Seven Years' War, and it was to both countries' benefit to keep up the alliance afterward instead of turning on each other once again - so royal marriages were needed to make sure that the monarchs of each side felt sympathy for and interest in the other and would be unlikely to duke it out instead of using diplomacy when there was a problem. After having thought of Austrians as the enemy for their whole lives, the French people did not flip immediately just because the heir to the throne married an Austrian princess, though.

On arriving in France, Marie Antoinette was quick to assimilate - she was famously stripped of her Austrian clothes and dressed in French fashions before entering the country, of course, and she made a point of speaking French instead of German. Her intended rooms in Versailles were still being repaired, and where the architect intended to put a huge double-headed Hapsburg eagle on the ceiling she requested a simple rose pattern - which sounds like a small thing, but every day a crowd would be there to watch her get out of and back into bed (the lever and coucher ceremonies), and would have seen her associated with the grandeur of Austria. These were very good symbolic steps to establish herself as a French princess. At the same time, though, the wedding/entry festivities in Alsace-Lorraine emphasized the hybrid Austrian/French nature of the marriage, impressing the fact of her foreign origins on both the nobility and commoners present.

Once at Versailles, Marie Antoinette continued to act in ways that marked her as a foreigner. She was impatient with the unfamiliar etiquette of the court, which had largely been set by Louis XIV a century earlier and which the French courtiers were used to. In the winter, she engaged in sleighing, an Austrian pastime that seemed very strange to the French. She drew a circle of court friends based on whether or not she liked their personalities, instead of whether they were people with positions that entitled them to her time. Sometimes she had conversations with Hapsburg ambassadors.

Even while she was still only dauphine, as the highest-ranking royal lady at court she had to deal with a lot of queenly baggage that many today don't fully take into account: most of the previous French queen consorts were seen in an incredibly negative light in France! They went through sex scandals, were repudiated by their husbands, they went down in history as vicious harpies. Those that had good reputations were saved in part by official royal mistresses that drew public ire as wasteful spenders and poor counselors. As dauphine, Marie could have come off well in opposition to Louis XV's mistress, Madame du Barry, but having a mistress around doesn't seem to have helped much - perhaps making it known through her decision not to speak to the other woman that she was unfamiliar with the French royal custom of infidelity rebounded on her.

However! Most of the negative feedback Marie Antoinette got as dauphine was from nobles at court and from her mother via letter/ambassador. Ordinary people might complain that she was a foreigner when talking about her to each other, but when she visited Paris, they loved her. (I suspect it's a letter discussing this that you came across?) Trying to walk in the Tuileries, where French subjects of all ranks were able to observe the royal family, she and the dauphin were mobbed. At the opera, when she broke with the tradition of not applauding, everyone clapped with her. A crowd at a state event in Paris cheered her beauty and grace. At this point, she wasn't yet loathsome to them, even if they would have preferred a princess from a country that was their traditional ally.