Is a girl who made a covenant with Allah to abandon a sin, then broke her covenant three times, liable for three expiations? And will Allah curse her for breaking the covenant, and is she considered among the hypocrites?

Falling into sin necessitates repentance and the fear of Allah. Fear after committing a sin is a sign of faith. Whoever breaks their covenant with Allah is required to offer expiation (kaffarah). The expiation does not multiply if you have not offered it for previous instances, because in this case, they overlap.