He, my client owns S Corp 100% and - allegedly by a former contractor - he did not follow through with a promised ownership offer. She, the ex-contractor, also alleges that he embezzled from an unrelated party (on a separate business matter.) She is furious and irate and possibly mentally unstable (words of the DA) and flooded me two weeks ago with 10 emails describing conversations with her lawyer and the local District Attorney.  

They engaged an attorney to mediate their dispute. That attorney has not contacted me.

I highly doubt she initiates me in a legal action or involves me.  She has not made any hints and seems comfortable talking with me and sharing her feelings, ugly as they are.  I assisted them with an ownership tax issues two years ago but he didn't make an ownership offer.  She has not asked me for advice  I don't know if a lawsuit has started.  

I anticipate that this 2023 S Corp return could be a part of a future lawsuit. I probably need to assume that the 2023 and prior tax returns will be evidence supporting her allegations.

What do I need to know to make my work "lawsuit-proof"?  I follow Circular 230 and the professional guidelines.

Should I hire a lawyer so that my communications with my client are protected?  

Should I contact AON for advice?

Anything else?

Hope for the best but prepare for the worst.