Welcome to Psych Central. Sorry your girlfriend is having what sounds like waking up depression. Has she talked to her doctor about this. It could be a medication problem or a lack of medication problem. If she wants to solve this problem it could be easy for you. If she does not want to solve this problem, I feel a lot of empathy for you but know no way to help someone that does not want help.
Some people at PC will find a therapist will help them. Some people find the forums give them the compassion and empathy they seek.
http://forums.psychcentral.com
There are articles that go into more detail about coping
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