Even though that girl was offended and it might offend some other people, if we do change the mascot some people might be angry because the mascot is part of their history.
Sports teams usually have a mascot because they think that person/animal/thing is fierce. Usually they don't mean to offend/make fun of their mascot but to kind of honor it.
According to cnn.com a lot of people are not trying to be offensive. Mascots can be part of a school's culture and may sadden some people if they are changed.