As long as the candidate does not have a record on the issue, and states that he/she is unable to answer questions re: abortion because they may be required to rule on them, it should be OK.
I think you're right. In that case, she'll just ask the nominee if he/she respects precedent, and of course they'll say 1) "Yes, I do", but 2) "But that isn't an absolute rule, or else we'd still have Plessy v. Ferguson rather than Brown v. Board of Education." To get her vote, the nominee just can't be on the record saying Roe is bad law. That shouldn't be too tough to do.
Collins isn't stupid. Okay, she is
kind of stupid, but even she knows that Roberts won't vote to overturn Roe. So she's making this statement as her version of virtue signalling -- "Yes, I know that Roe really won't be overturned, but this is my chance to show everyone how pro-choice I am."
I'd be shocked if she didn't vote for the nominee.