Jasper introduced his new girlfriend to his adopted family finally. They took to his very human girlfriend well, except Rosalie. Rosalie felt threatened by her for an odd reason, eyeing the already skittish girl like a Hawk. Emmett and Edward suggested that Jasper keep his ‘twin’ on a short leash for the night

Jasper gave a stern look “Rosalie. Be nice.” he warned his sister, seeing and feeling the amount of disdain she had for the new girl