The fact that your girlfriend feels comfortable enough telling you about her dream just means she's unlikely to act on any of these impulses. If she seriously considered leaving you or cheating on you, she surely wouldn't drop hints ahead of time. You don't have anything to worry about. We've all had strange dreams, most of which don't make any sense even whilst in the dream.

No, I wouldn't be bothered by either because as you mentioned dreams are out of our control and are basically just the subconscious doing whatever the hell it wants, often impossible things that shatter reality.

However I would be bothered if my partner told me because this means that they attached more importance to it than there should ever be.

On the one hand it may be good, you may have a very pure partner who feels incredibly bad about such a thing to the point the partner simply can't stay quiet about it or it would eat them up inside as if they stabbed you in the back and that's great.
It's the other option that's the problem. The one where the partner tries to gauge your reaction to the revelation. It could just be just the tiniest bit of insecurity or doubt that may or may not fester...or it could be major doubt the right choice was made or even a test that ruins the relationship.

I'd probably just choose to shrug it off and keep going as if it was never mentioned (other than mentioning you just consider dreams to be dream and nothing more). This sort of thing isn't important enough to affect a relationship...and if the other party thinks it is then the sooner this ends the better so one shouldn't fight it either.

dreams are like Vegas
Edit: Keep up the good work with Crash :D

I've had fucked up dreams about things I'd never even think of doing. I won't even tell you about it...
The point is, the human brain and its consciousness is a mysterious thing. We can't control it while sleeping; or at least, we rarely can.

When you are having a dream, it does not necessarily means that the dream reflects anything you would want to happen in real life. As an example, when we are having nightmares, it isn't because we want it to happen, but because it is a simple accumulation of thoughts about anything you have seen, or could imagine in your life.

Her dream was most likely an accumulation of thoughts from the past; having a crush on another person. It is nothing but memories running through her mind subconsciously, memories from either the past, or simple imagination.
Dreams do not represent the real world in any way. They simply reflect it.

Partner being unfaithful in dreams = will be unfaithful in reality

She even told you that? Be sure that she does not think only of you during the day

A dream is a dream is a dream. I have done naughty things in dreams and I have done terrible things in dreams and I don't give a second thought to it because that is exactly what they are, dreams. Of course it feels nice if you feel you are close to someone in a dream and it feels horrible if you kill someone in a dream and so on; does it mean something? Not really.

Its too late, you have to end the relationship, Im sorry...

:(

In my opinion

I almost always dream of people being mad at me or me screwing something up.

Often when I'm awake I have trouble remembering that bad thing wasn't real.

99% of the time you have no control over whats going on in your dreams.

Tomorrow you'll probably dream about french fries is potato land.

Stop worrying. The brain is weird.

My honest answers would be slight concern for both. I've had plenty of my own dreams that really worry myself and don't even know why they happen. I've had dreams where I can actually feel everything happening. Control over dreams would be nice but not everyone can do them and not all dreams can be desirable. All I know is that if it were to happen in my own relationship then I would want to talk about it a bit.