As far as a lightsaber battle would go, that would be interesting. Leneer was able match Malgus in battle twice even landing two strikes on him, so I believe she is in the same league as Asajj. In the force however I don't see Ventress overpowering Leneer. Leneer was only ever truly injured by force powers when she was subjected to powerful force lightning and even then she was able to block it the first time. And since asajj cant create lightning I doubt she could overpower her. Perhaps Asajj coud break through her force shield and choke her out but Aryn was able to overcome Malgus force grip so I believe she could over come Ventresses as well