How do I help my girlfriend?

Hi all

My girlfriend and I have been together 6 years. We've had some issues lately but getting things out in open lately.

My issue is that pretty much the whole time we've been together she gets angry with stuff, me, her parents, work colleagues etc. She can be really short when she speaks to people at times. She often complains about people at work and sometimes I'm not sure if these people are as bad as she says.

She has a good female friend at work who's former partner I kind of know. He's always seemed like a really nice guy but since they split up apparently he's the worst person possible. When I met this work colleague of my gf she reminded me of my gf and I could see why they're friends. It made me think that this girl and my gf are both the ones in wrong??

I've tried to talk to my gf in past about being positive and getting what you want out of life and if your perception is different then things don't have to be bad. She gets wound up about stuff and takes it out on me and is suspicious of me trying to help as if I'm trying to manipulate her...in totally not!

We do have good times and she can be nice and sweet (she was always like this to begin with), I just don't know how I can help her or if she will change??!!