My girlfriend scares me when she gets her period?

First of all if you really care about her, don't leave her for her period. Trust me its a girl thing even if they don't admit it, girls like to see how much their boyfriend is going to put up with.Thats what I did and my boyfriend left me, trust me if you still love her don't leave her because of her moods.sorry but it happens

You really can't do much about it.
It's what happens. I don't really have those extreme mood swings and stuff, but some of my friends do, so when they do, I just try not to say anything which would make them angry or sad, and just keep up normal conversation.
You have to remember that the things they (your girlfriend in this case) say/says, is not really what she means.
She's just blowing off steam created by her hormones.
Just play along until she's better.
You'll have to do this every months but only for a few of days.

Play dumb! hahaha xD

Why not just keep your distance when she's on her period?

be usually nice to her, don't do one single thing to make her mad.open the door for her, blah blah blah

Hello to PMS world:) You just accept that this happens but you lay down some ground rules for it too. My Girlfriend has PMS and it used to be quite intolerable until we sat down and talked about what would and would not happen.

Rule #1 was that I was not to take anything hurtful she did or said during her time too seriously.

Rule #2 was that she knows she is being moody and will attempt to control what she says and does.

Rule #3 was that I could go elsewhere if rules #1 and #2 were being violated.

The main thing is that you both understand that there's something biological going on and that's the cause of the grief and not anything going on between you.