I would think she needs some sort of training to be a counselor. To my knowledge K'Ehleyr has no background in psychotherapy. As for advising the captain, he has no shortage of those. Though one skilled in diplomacy would be a plus. Wasn't Troi on the bridge because she was an empath and Picard figured that would be useful? A Captain's prerogative type thing?
Though as an Ambassor K'Ehleyr could overrule and second guess Picard in certain situations. I can't see any Captain wanting that. I'd require her to resign her postion as an Ambassor and join Starfleet first.