What should I do regarding a teacher who wears clothing that describes her 'awrah, given my fear that advising her might lead to undesirable consequences such as her preferring me over other students or vice versa, especially after some time has passed since this issue began?

A woman wearing something that describes her 'awrah (intimate parts) is a great reprehensible act that contradicts the Shar'i (Islamic legal) dress code and subjects her to the warning against the mutabarrijah (a woman who makes a wanton display of herself). It is obligatory to condemn reprehensible acts for those who are able to, and silence is not permissible except for a legitimate Shar'i purpose, such as fear of a greater harm. Abandoning enjoining good and forbidding evil without a legitimate Shar'i justification is dangerous. If the abandonment of condemnation is due to fear or an illusion of harm, then repentance is obligatory. However, if you genuinely fear actual harm, then there is no blame in remaining silent. If the teacher persists in her state, try to empower righteous female teachers and those whose words might influence her.