I would sit down with her face to face and ask her point blank if she is happy in your relationship. Give her the benefit of the doubt to open up. If she's honest maybe you can salvage the relationship. I don't know what exactly was said, so maybe that isn't a possibility for you. If she's not honest with you then just tell her you have reason to believe she's really not happy and that maybe its best to end things.
So, so you think you can tell Heaven from Hell,
blue skies from pain.
Can you tell a green field from a cold steel rail?
A smile from a veil?
Do you think you can tell?
And did they get you to trade your heroes for ghosts?
Hot ashes for trees?
Hot air for a cool breeze?
Cold comfort for change?
And did you exchange a walk on part in the war for a lead role in a cage?