Just don't do anything as a surprise - make sure the person understands the possible outcome - and give her enough time to reflect your position. She might thin

Just don't do anything as a surprise - make sure the person understands the possible outcome - and give her enough time to reflect your position. She might think that she's doing good for the company, even if she have to argue with you, and she might be actually right, but at the end, it is you who is paying so you're the client - so make sure the service provider understands what are your needs - including things like "don't argue with me, even if you're 100% sure my decision will harm the company". You mentioned personal conflict - so this might be arguing on some irrelevant subjects. Even in this case, it might sound odd for her but she should clearly understand your PoV - "Justin Bieber is better than Led Zeppelin, if you disagree vocally, I'll fire you!" - again, this might sound odd to her, but it depends on her compensation package whether she accepts your conditions or not.