بِطَغْوَاهَآ

بِطَغْوَاهَا is a phrase (شِبْهُ الجُمْلَةِ), a genitive particle followed by a possessed noun and a possessive noun

PhraseParticle / Noun / NounNounNoun Particle
شِبْهُ الجُمْلَةِجَارٌ وَمَجْرُوْرٌ وَهُوَ مُضَافٌ وَ مُضَافٌ إِلَيْهِمُضَافٌ إِلَيْهِاسْمٌ مَجْرُوْرٌ وَهُوَ مَضَافٌحَرْفُ جَرٍّ
PhraseCompoundPossessive PronounGenitive noun + Noun possessedParticle of pulling down
  
by their transgressionبِطَغْوَاهَآ=هَآ+طَغْوَا+بِ
by the transgression of theirstheirsthe transgression ofwith/by
Surah/Below is the only verse in the holy Quran containing the genitive particle and nominal compoundبِطَغْوَاهَآ
Verse
91-11Thamud denied by their transgressionكَذَّبَتْ ثَمُوْدُ بِطَغْوَاهَآ