What should a girl do to repent and commit to prayer, when problems between her and her sisters have recurred every time she has tried to do so, making her feel that God is displeased with her?

Repentance to Allah is immediately obligatory for all sins. Do not give Satan a way to make repentance difficult for you or to create enmity between you and your sisters. Rather, seize the opportunity and continue your repentance, seeking help from Allah. Fear Allah regarding your sisters, treat them kindly, and overlook your rights for their sake, for forgiveness and reconciliation have a great reward with Allah, as He Almighty said: "And the retribution for an evil act is an evil act equivalent to it. But whoever pardons and makes reconciliation - his reward is [due] from Allah. Indeed, He does not like wrongdoers."