She could be...I wouldn't say so right off the bat but the chances of that actually happening is somewhat likely. Of course, it could just mean that she doesn't actually know that you are his girlfriend and thinks you're a random person. Or it could mean that she just wants to be friends with just your boyfriend (and not you) not because she wants to steal him away from you but rather she just doesn't like you for whatever reason or she doesn't feel close to you yet. But then again, it could mean that she doesn't like you because she wants your boyfriend.
So be aware of all the possibilities. Look for her body language when you guys are actually seeing each other in person. Does she seem a bit timid to you or does she totally exclude you from everything? If she is timid, it may be because she doesn't know you yet and you should maybe try to befriend her. If she's excluding you, she probably means business that she doesn't like you, whatever reason it may be, and you should stay away from her. Also warn your boyfriend about her too.