New Work Mates

Why is it when a new person starts a job with you, they suddenly feel they know more about things than you do? I work in a library. We have 30 branches. Recently a woman from another branch was hired to be the office manager's new assistant. She seems like a very nice person. However, she likes to compare the way we do things with the way the other branch does things. Their branch was bigger and each branch does some things differently. She seems to want to change things to suit the branch she came from. "At so and so we did it this way" A small thing sure, but it is annoying! Why can't some people just try to get used to the new job environment and get to know the employees before they make such broad statements.