People who can manipulate the power of the warp, if they aren't a sanctioned psyker from one of the major Imperium organizations (Astra Telepathica, Astra Militarum, Navis Nobilitae, and so on) are widely viewed as heretical; and as such are usually hunted down by good law abiding Imperial forces and hated by the average citizen of the Imperium. In fact, sanctioned psykers are often suspected and/or hated by many of the Imperium as well, with some organizations, like the Ecclesiarchy, even willing to hunt down sanctioned psykers in the pay of powerful groups like the Inquisition.
That being said, on almost every Hive World there seems to be a burgeoning black market with some form of psyker/chaos/xenos element. FFG's Dark Heresy series and a number of the Black Library books have instances where rich nobility, displaying deviant and/or sybaritic tendencies, dabble in these extremely heretical circles for their own various reasons. So it's not unfeasible that a noblewoman seeks out a sorcerer that's infamous in the undercity - but she'll have to do so very, very discretely and quietly.