This is a trascript from a podcast I was listening to. The woman was asked about what she thought was the hardest aspect in learning english, to which she replied

> 
> 私が困っているのがはつおんですね
> 
> 
> 

So... why 私が instead of 私に (meaning 'to me'). Not only that but, what is the role in the sentence of 困っているの? It is the continuing action conjugation of 困る (to worry) but how does it fit in the sentence? And what is the role of の?

Thank you very much.