"I assisted them with an ownership tax issues two years ago but he didn't make an ownership offer."

"Them"?

Sounds like she was a client at that time.  She may be claiming conflict of interest.  If you're not a party, you're at least a witness.  I'm not sure how your malpractice insurer would become involved, if a non-client is suing you.  But first you should figure out if, when and how she was a client.