What is the ruling on one who believed that horoscopes are a science and did not know that it is a claim to the unseen, so is she excused by her ignorance or does she become an infidel, especially after the hadith reached her: "Whoever comes to a sorcerer or a soothsayer or a diviner and believes him in what he says has disbelieved in what was revealed to Muhammad," and she claimed that she did not know?

These are whisperings from Satan. There is nothing in your aunt's words that necessitates her disbelief (kufr). Her belief that astrology is a science, like physics and chemistry, is a sound belief. Some sciences may indeed contain elements of disbelief. Furthermore, her statement "I did not know" is not disbelief, as it can be interpreted in many ways. A Muslim does not exit the fold of Islam except with certainty. Therefore, fear Allah and refrain from declaring Muslims disbelievers.