Can repeated rejection of marriage proposals by a girl be attributed to sorcery (sihr) performed on her, and what is the ruling of Islam on this, and how can it be treated if it is indeed present?

The person proposed for you is one of two types: Either he has bad characteristics, in which case it is good to reject him, but one must be careful not to pry into people's inner thoughts, for we have not been commanded to do so; the judgment is based on outward appearance. Or the rejection is an illusion due to envy (hasad) or magic (sihr), known as magic of obstruction (sihr al-ta'til), and its solution is to accept a husband with good characteristics whom people of religion recommend, or by performing ruqyah شرعية (Islamic exorcism) to treat the magic.