Am i over her? how do you know when you're over an EX?

So, in relation to the girl i'm 'seeing' who tells me she isn't ready for a proper relationship due to not being over he EX.

It's made me ask myself, am i over my ex?
She split up with me in september, but, what does it mean to be 'over' someone?

I can't lie in saying i don't miss being with her, we had fun, maximum confidence with eachother, and always made eachother smile. But it's been 3 months since i've even spoke to her, and if she were to ring me up right now asking for me back, i'm not sure i'd want to be with her again, i don't know if i honestly ask myself.

Is to be over someone, for them to not even cross your mind? or is it natural to still think of EXs and miss them even though your over them?

What i'm asking overall is, what does it mean to be over someone?

You are over your ex when you think about them less and less. Or perhaps you're over them when you have the opportunity to see them and you really don't care.

Sounds like you are over your ex.

Maybe seeing (imagining) your ex with a new partner and not having any bad feelings about it, is an indicator.
It could be tricky with "thinking" indicator. It is natural to remember moments and people from your life and sometimes (not regularly!) it can be an ex, even when you trully don't want to get back together.
Accepting that it's over and no matter how good it was, you would never want to be a couple with an ex again.

On the other hand, it was a reason why you've been together, something that made you like him/her, it could be something permanent, that you may still like (you would like again) about them.

It is natural to still recall good times with an ex and think about them fondly sometimes. But I think the best definition of being "over" someone is where you are in your life. The desire to get into a relationship with someone else and the desire to make it work with the new person. Not a rebound, though.
In many ways, breaking up is similar to the grieving process. You have to work through the stages before you come out the other side. And everyone grieves a little differently.