The Medrash itself seems to answer that. It wasn’t of sacrifice alone, rather it was the act of the vatrunus that it included. Hashem said that Klal yisroel had worshipped idols to which Rochel said that when my husband was being taken away from me, I helped my sister not get embarrassed, therefore you Hashem should turn away when idol worship is being done. It is the same concept of turning away from what belongs to you alone being taken away and not protesting.