My little sister witnessed something that telepathically comunicated to her that it was God. It looked like a shepherd, and had a cain, and a robe, and was an old man, with a beard. She also said It glowed.

I don't understand why this would take place. I also know that Anunaki pose as angels, or holy things. I also know no man has seen God, the only thing even remotely close, was Fatima. Also, my little sister was never even baptised.

Is there any way I can find out whether it is evil, or good?

I remember her saying it had an aura around it, and that Anunaki have some kind of aura around them.

The fact that it said it was god is a clear indicator. It was using images in your sisters mind to project itself as something favorable, something that she would recognize and easily follow. More then likely it was reptilian or some negative entitiy.

No honest, light or "good" entity would ever claim something like being God.

Interesting that your sister is being involved in this as well. Seems like some things have taken an interest in you. Don't feel special :p As some beings very wise say, "Information protects". Inform yourself.