What does “ground” mean in the context below? (from Michelle Obama’s Beginning)
Craig, my brother, in his ambling and smiley way, had conveniently broken every trail for me. I had aways been known as Craig’s little sister. Now, though, I was just Mitchelle Robinson, with no Craig attached. At Whitney Young(her new high school), I had to work to ***ground*** myself. My initial strategy involved keeping quiet and trying to observe my new classmates.
Is “ground oneself” an idiom? Thanks in advance for your answer.