This is difficult I can't give TMI as I do not want to risk being outed.....
Basically colleague and I are both the same level and both manage teams of people.
She is always bigging herself up and slyly trying to put me down to our boss. She is extremely clever at this. I am quite a straightforward person, I just want to do my job and do not want to enter into the competitive arena of office politics. So far, I have risen above it by ignoring all comments or taking them at face value. It is really difficult at times and quite draining working in such a toxic atmosphere. We share an office and have to work together on quite a lot of projects, so I HAVE to get on with her.
Have you actually spoken to her about it? I'd suggest asking her for a meeting, perhaps off site with a coffee if that's possible, and saying you've noticed this behaviour, not sure if there is a problem, but because it's important you get on as you work together closely, you thought it might be a good idea to have a bit of a clear the air chat.