Ive got a 4 year old boxer that is scared of everything help. i have had her since she was a pup?

Jess that is her name. she is scared of loud noises and even something in the house that is a different spot she has never ever been abuse but she was the runt of the litter with extremely bigger pups that would of picked on her (i don't no this for shore but i think it may have something to do with it) and when she comes into contact with another dog like when someone comes over and they bring their dod jess gets really psycho like she runs round like crazy but that isn't the problem the problem is she gets violent with the other dog as if she is scared so much that she has to get the other dog to the ground and if you have been with a boxer you would no how strong they are.