Legal Question in Business Law in California

Absolutely not, for a lot of reasons. I doubt the company really told her that, and if they did they're idiots. They could, however, fire you for it if you are still working there.

The company is probably bluffing in the hope that your friend will back down. Probably.

Nothing you've written suggests that the company has a viable claim against you, or that losing your friend's lawsuit would create one. I can imagine circumstances where it would, though. They don't come up often, and I don't have enough information to say whether they're present here.

Sometimes businesses or individuals who have no grounds for a lawsuit decide to sue anyway. That's usually because they mistakenly believe they have valid claims, but sometimes it's done maliciously. Either of those things could happen here. Litigation can be an ordeal, even if you win.

As I said, I have no reason to think the company has grounds to sue you or that it would actually do so. Based on the limited information I have, the risk seems quite small. But a business rash enough to make this kind of threat might also be rash enough to go through with it.

I agree with the previous answers, but would add that "can they sue me" is a different proposition than "can they win?" You might be called upon to defend a baseless suit that you would win, but at some expense and a lot of time and effort.