Basilisk: Kouga Ninpou Chou + FILM : Shinobi

[Jeff_from_MD]

If somebody can form poison into her breath, canceling that power doesn't make the poison to affect the person herself, instead.

yes, oboro CANNOT turn kagero's poison technique against herself. BUT, Kagero technique might be not only to harbor poison, but also have a slight resistance to it?

Oboro stopped Kagero from using the poison, and also stop Kagero's resistance to Tenzen's poison. Although that's just another guess. Another possibilty is that Kagero's resistance to her own poison dissappeared as well,

[Aeon]

For some reason I don't think Tenzen used poisen at the end of the needles. I seriously doubt that poisen needles would make Kagero scream like that, she is a trained ninja after all.