im cxertain that you can do it.
just remember to tell her that she deserves happiness, and i think that she deserves someone like you because you care so deeply... you even know how she's like day by day in detailed manner.
i truly think that to really make her happy, whatever that caused her to begin thinking negatively has to be dealt with.
and i know that you have what it takes to change her life for the better.
If you need some advice or even just a friend, i'll always be here.