Was any engagement letter signed by both you and her, however simple that may be?  If so, there should be terms for disengagement, failing which, you probably won't have grounds to fire the client.

If no engagement letter was signed, there is no engagement to begin with.  Accountants screen clients all the time for various reasons (e.g. conflict of interest, risk profile, etc.).  Depending on the situation, especially for risk profile and PITA, the way employed to turn them down may be more subtle (and domestic) than saying no right out.

Bottom line is, you don't have to accept every single client who walks in.