As for marriage, personally I would vote for Ferdinand II of the Two Sicilies. The right age group, and born of Marie Antoinette's favorite sister Maria Karolina (whose daughter, Maria Amalia, was originally promised to Louis XVII before marrying the Duc de Orleans after the Revolution). Franz Karl would also be interesting - he was supposed to inherit the throne of Austria-Hungary after his disabled brother Ferdinand abdicated. He was bullied out of it OTL by his ambitious wife Sophie of Bavaria, who wanted their son Franz Josef to become Emperor. If Titi marries Franz Karl, Sophie could marry her good buddy the Duke of Reichstadt (ironically the son of Napoleon and a second cousin once removed to Titi). That right there would make for super fun family reunions.
As for her education, I looked first to the education of women in the French royal family. Her aunts, Èlisabeth and Clothilde, were educated in "They were given the usual education of contemporary royal princesses, focusing upon accomplishments, religion and virtue... They were tutored in botany by M. Lemonnier, in history and geography by M. Leblond, and in religion by Abbé de Montigat, Canon of Chartres". So with accomplishments, we can assume the traditional feminine accomplishments of the day: needlepoint / embroidery, drawing, singing, dancing, music. Titi's maternal grandarents and her mother were devout Catholics, so she definitely would have a heavy Catholic education, particularly virtues: chastity, kindness, charity, devotion. Marie Thérèse shared the same governess as her aunts, Marie Angélique de Mackau, who would unfortunately be dead at the time of Titi's upbringing, but left behind two daughters both close to the French royal family: Renée Suzanne de Soucy, who was considered strict and intriguing, and Marie-Angélique de Bombelles, a famous letter writer and close personal friend to Princess Èlisabeth of France.
On Marie Thérèse's maternal side, education also seemed to be conventional. Marie Antoinette's education involved German, Italian, Latin, and French; her education also involved music. "Maria Antonia developed into a good musician. She learned to play the harp, the harpsichord and the flute. She sang during the family's evening gatherings, as she had a beautiful voice", which reinforces the 'accomplishments' portion of previously mentioned.
So for the Princesse Thèrése Antoinette, I would assume a fairly traditional education: music and dancing, the arts (drawing, painting), embroidery, religion and religious virtues, languages (Latin, German, Italian, maybe Spanish), geography, some history, writing / spelling / reading, and 'poise' (courtly manners, etc). Her parents might chose to beef it up as -I'm assuming- she's their only child and they might choose to indulge her - one of Marie Antoinette's sisters, deemed unfit for marriage, did scientific experiments and research with her father's blessing. Her maternal grandfather had a passion for astronomy, so that could be easily added in with his blessing. So I'd stick with the traditional outline, but if she's particularly bright or gets a particularly bright governesss, I could see some more topics being added in: botany, philosophy, politics, etc.