What is her motive?

[TEF]

Then theres 'its was a test' approach, where she would see if she could make Jack rest and divert him from his mission. The smirk at the end could be her happy that pretty much nothing would stop him from getting Aku.  Don't usually fight with someone half assed then run away and give an evil smirk if there isn't an alternative motive.

I think I agree most with this point of view. This series was really very thorough (perhaps too thorough for its audience) so I wouldn't doubt any of the more "overanalyzed" theories. It truly was a shame to see it canceled, but there's still hope.