I don't remember seeing this when it was posted. Sorry about that Escarabajo.
She might have been upset if we had been late.
Se pudo haber enojado/molestado si hubiéramos llegado tarde.
She might have been upset, but we were on time.
Se pudo haber enojado/molestado, pero llegamos a tiempo.
She could have been there if she had planned her day better.
Pudo haber estado allí si hubiera planeado mejor sus tareas del día.
She could have been there, but she planned her day badly.
Pudo haber estado allí, pero planeó mal sus tareas del día.
The accident could have been worse if the road had not been empty.
El accidente pudo haber sido peor si la carretera no hubiera estado vacía.
The accident could have been worse, but the road was empty.
El accidente pudo haber sido peor, pero la carretera estaba vacía.
The world could be better if there wasn't so much violence.
El mundo podría ser mejor si no hubiera tanta violencia.
The world could be better, but there's too much violence.
El mundo podría ser mejor, pero hay mucha/demasiada violencia.
Espero te ayude.