How to tell if my rat is injured?

I walked into my room about an hour ago to find my little brother squeezing my rat so hard it was squeaking in pain. I got the rat out of his hands and put her back in her cage. I had (finally) just managed to get the rat to trust me, but now it's cowering in the corner of the cage and refuses to come out. I took her out anyways just because I wanted to take a look at her and make sure she was still walking okay, she was, and as soon as my brother let go she stopped squeaking. I'm still worried though that he may have hurt her. Is there any way I can tell? And will the rat never trust people again now? =/