Plagiarism question...please help me!

I've no idea where you stand legally but if ethics and the reputation of your business mean anything to you then clearly you should support B and get rid of A. You don't need someone of such poor character on your team and they will be a poor investment long term.

I'm not sure I understand this situation. As I see it, you and your colleagues - A and B - all work for the same outfit (let's call it XYZ Corp.). If that's the case, then the product doesn't belong to A or B, it belongs to XYZ Corp. It doesn't make much sense to me to have A going around saying that the materials are hers. They're not, but then they're not B's materials either.

As such, this isn't so much a matter of plagiarism as it is a matter of A claiming credit for something that she didn't do. That's a problem, but that's an internal personnel problem for XYZ Corp. Customers shouldn't have any concerns about that. In fact, B might be the bigger problem - threatening to take an internal matter to external authorities is a possible PR disaster. That can't be allowed to happen. Sounds to me like A is a jerk and B is a loose cannon. Both need to be reined in.