Problem with a colleague

Hi there
I think my colleague is bullying my other colleague.
She undermines her work to clients and to our other colleagues. She often complains to me about her and to our boss who she happens to be married to.
The girl who is on the receiving end has lost a lot of confidence. She is busy looking for another job. She is not the first or even the second person to leave the practice and use this person as the reason.
I try to stay out of it. I do my work and make sure to stay on the good side of this person. Most of the time me and her work well together although it takes effort from me.

The latest episode has really gotten to me. Our client doesn’t want to see the junior colleague because they got the idea she messed up the consult. It seems they got this idea from the possible bully.
She says she didn’t tell them that she had effed up but that she had been angry about how it had been handled.
She says in a meeting of the 3 of us that she is sick of covering up for this girl and she won’t do it anymore.

I have now spend 8 days obsessing about this meeting. The way I see it there wasn’t actually a mistake made. She didn’t check her facts and perceived a mistake. And let the client believe it too.
I can’t seem to stop thinking about it and my constant obsessive thoughts have ruined my weekend and led to loads of buffering.
I keep having imaginary conversations with her about this. I land up feeling so angry. I’m also angry with myself for not managing my mind better.

I feel like I must do something. She can’t get away with this.
But I’m also scared of her. She could make my life a misery. I once tried to argue with her and was put very smartly in my place.

The issue is I’m meant to be buying into the partnership so I would be her boss and her husbands partner (with one other partner) but she is almost 20 years older than me and I am really not sure I can manage her. I’m a recovering people pleaser. I want to step up to a bigger version of myself but I doubt my ability in this situation. Besides the fact we all know we can’t change people.

I’m beginning to think what’s bothering me is my inability to stand up for my bullied colleague in these moments. I think I prefer to stay the golden girl and not be lumped with her but I’m ashamed of that.

I want her to change but she’s unlikely to. If I change how I work with her I might make my job more difficult. But if I keep quiet I am unhappy and inauthentic.

Instead I just obsess.

Can you help me direct my mind?

Thanks so much