That experience (with the lady who "stole" your client firms) points out
the need that when training someone, or in any other busines dealings
involving possible taking of your business, you should always have a
"non-compete" clause in an agreement that any work she does for any
of firms you have dealt with in the las 1-2 years will be a violation, and
that any such work she reports to them would be you work product and
the fees owed to you.  The companies can be provided a copy of such
and if they violate, they may be sued for possible damages.