[X] Stick with the usual, atomized contact you would use for every hostile source. Multiple small cells using a few of her contacts each, with each of her contacts beings used by multiple cells, so that the overlap can be used to find out any duplicitous contacts or to notice when a cell might have been flipped. Devils in service of Baator are no more risky in that regard then any other contact from a high-magic realm with it's own security apparatus.