A Supreme Court nomination, especially under highly controversial circumstances like this, is a major vote, like a vote to go to war. I would tend to agree that the specifics of a Senator's voting record tend to be forgotten but major votes are remembered. Who voted for the Iraq War, for instance, remained a charged campaign issue for many years afterward.
Furthermore, she gave a grandstanding, highly partisan speech in which she went all in for Kavanaugh and blasted Democrats. That will be fodder for attack ads later. Now she is saying she doesn't believe Dr. Ford. That, too, will be remembered.
Collins has enjoyed high approval ratings in Maine throughout her career but they have slipped considerably during the Trump era. I predict they will become worse after this. And activists in Maine are not going to forget.
https://www.cnn.com/2018/10/05/politics/susan-collins-2020-challenge/index.html