She doesn't actually call him bro btw. That was how the translator translated the MC's choice of pronoun (the masculine and casual 'ore' in this case).
Folks might also be interested to know that she also uses お前 (omae, a form of "you") to refer to the the hero, which in modern Japanese is a rather masculine casual/rude thing to do. It's most typically seen with guy friends speaking casually with one another, although it can also be used to start a fight with someone.
Damn, that must suck to be unwillingly reincarnated as a farm girl and realize that the other guy reincarnated as a hero, despite being less knowledgeable (lol) about video games. But it's amusing, though.
@a707 “Ore” is a masculine personal pronoun, used by our protagonist to put emphasis on being a guy. You must be thinking about “omae,” which, as explained by redpandamaniacal, is the casual/rude way of referring to another person, especially between two guys. What do you think a better way to convey that idea to an English speaker would be? Dude?
I think from our MC's perspective, it really sucks when you end up with a nerfed farm girl body/avatar while some noob gets to have the OP hero body/avatar.