What should the questioner do regarding her assumption that she used to mix up the Sunnah of Fajr and the Fard (obligatory) prayer of Subh, and will Allah be angry with her despite her previous repentance?

All praise is due to Allah, who has guided you and accepted your repentance. As-Subh (Dawn) and Al-Fajr (Daybreak) are two names for one and the same entity, which is the obligatory prayer enjoined by Allah after the appearance of the true dawn (Al-Fajr As-Sadiq). If you pray two rak'ahs before sunrise with the intention of performing the obligatory Subh prayer, then you have discharged your duty and fulfilled the obligation. What is prescribed for you is to pray two rak'ahs as the Sunnah of Al-Fajr after the appearance of the true dawn, then two rak'ahs with the intention of performing the obligatory Fajr or Subh prayer, then engage in the remembrance (adhkar) of the prayer and morning, and recite the Qur'an. It is better to continue in remembrance until sunrise.