Will the repentance of a girl be accepted, who apostatized from Islam, practiced homosexuality, reviled the religion, and described herself as a disbeliever every time she uttered the Two Testimonies, especially since she had sworn to disbelief, intending it?

Yes, she has a way to repent, and her oath does not stand between her and returning to Islam, especially since she swore it after her apostasy from the religion. And whoever repents, Allah will accept his repentance. Repentance is available for the apostate and other disbelievers.

As for informing her suitor, if you discern a sincere repentance from her and steadfastness in Islam, then you are not obliged to inform him. However, if you have doubts about her situation, then you must inform him of what you know about her condition, as a form of sincere advice to a Muslim.