Answer: Non negotiation and identity management
Explanation: Identity management theory is about maintaining the "self" in different situations. Depending on the situation, different ways or strategies of handling oneself may be taken, such as emphasising competence in certain circumstances when some competitiveness is at sake, for example, then perseverance and keeping one's attitude even though there are "tips" and "pressures" not to act as we usually do, or a friend's advice that hair colour is not appropriate, as in this case. It is important to maintain individualism in endangered identity situations.
Negotiation technique is by definition one with which no agreement is reached, that is, a compromise on an issue. So here too, Sadie doesn't want to compromise on her hair colour. This is the opposite of the negotiation technique where identity, as well as many personal aspirations and personal images, fit into a particular, say, cultural or aspect of a group, organisation, etc. So when there is no compromise about personal choice in some aspect of oneself, then there is non negotiation.