” She has a chiyuv of hocheiach tochiach es amisecha. She’s not being selfish, she is doing what the Torah requires her to do.”
That is in the case where something is a clearcut issur (such as seeing someone be mechallel Shabbos on purpose). It certainly does not apply to someone who is doing something with which she “philosophically” disagrees. Let her not do it herself, if it bothers her. But if someone wants to eat something fleishig and she is a vegetarian, she has no right to give him mussar and use “hocheiach tochiach” as a justification for doing so.