I would have you step back and reflect on your analysis of what’s actually going on here. One possible interpretation is the one you offered - that your colleague is hyper-competitive, which is creating problems for the team. But there are other interpretations, equally possible.
- Perhaps your boss has brought this colleague onto the team for the explicit purpose of shaking things up by challenging her peers. Perhaps the boss has concerns about the team’s performance, which s/he is addressing indirectly by inserting this new person.
- Perhaps the colleague continues to behave as she does because she’s receiving rewards from the boss for her behavior.
- Perhaps your other teammates are feeling put on the spot by her direct behavior, and in their defensiveness they’re labeling her as the problem.
Your challenge, as I see it, is to look in a more nuanced way at things and see what others (your boss, your teammates, you) might be contributing to the situation.
One positive step would be to have a constructive but direct conversation with the colleague aimed at understanding the intentions behind her behaviors. You might also initiate such a conversation with your boss, to understand how he/she sees the team’s performance and how his expectations of the new colleague fit into that.
In short, managing this challenge offers you an opportunity to grow by going beyond your initial assumptions and reactions. It’s entirely possible that your initial analysis is accurate and that your new colleague’s style is simply too aggressive, and if so, taking the exploratory path I suggest will help you stay centered in your reactions to her.