Your secret weapon: potential form
Here is what I would say if I were in a similar situation:
Honestly? Yeah, you can be.
Critical portion bolded. If your friend is determined to play the victim, there isn't going to be much you can do to prevent her from doing so. But saying that she has demonstrated the capacity to be mean and a bully accomplishes a few things for you.
First, it elides a lot of the victim mentality. You're not passing judgment on her as a complete person, you're pointing out that you've seen her act that way and so yeah, you can see how someone might form that impression of her. By shifting the discussion away from things she fundamentally is you can instead talk about things that she has done. If she wants to try explaining those things away that's her business, but laying out things that 1) definitely happened, and 2) people perceive as mean and/or bullying behavior makes it clear that it's not about people ganging up on her-- it's about how she acts.
Second, if your friend is only looking for validation of her behavior (as suggested in another answer), this lets her feel some of that without allowing her to just dodge the issue. She isn't fundamentally a bully all the time (perhaps; I don't know her), and some people might truly be unfairly critical of her. But talking about specific events brushes all of that aside. However many unfair situations there might have been, those specific examples are not among them. You'll have something specific to talk about, not a pile of subjective opinions informing your impression of her overall character based around all the things you recall her ever having done.
Finally, if your friend is legitimately unhappy with those issues being fair descriptions of her, this framing makes it easier to see a path forward. "You are mean and a bully" sounds like she has to start changing fundamental, deep flaws within herself, which is a big goal. "You can be a bit mean and bully-ish sometimes" sounds like those negative traits are real but just a small part of herself as a person, and she's already got plenty of better behavior to expand upon. It's a much more manageable goal, and identifying situations where those qualities tend to come out can help her improve.