Presumably, she knows that she will face little penalty for rebuffing Trump or McConnell on the issues they have for which the right position is unpopular - since there isn't much of a chance of her being dethroned by a right person.
I do take your point that the dynamics can be weird and aren't always "go to the median". And perhaps having a weird dynamic where the introduction of a different voting strategy or other party changes things dramatically - is not a good thing for trust.
Murkowski probably wins with RCV. The one D on the ballot, Chesbro, is a placeholder nobody expects to win, but her voters will surely rank Murkowski #2.
If i look at my country's upper chamber, which is elected with two-round system, then it is quite the reverse. Extremist candidates rarely pass to second round and if they do, they are eliminated there.
This isn't hypothetical -- you can look at the results in Seattle's City Attorney race, which strangely ended up electing a Republican to a citywide office for the first time in 20 years, and where the outcome under RCV would have been the same because the moderate candidate (the reasonably well-liked incumbent) didn't secure enough first-place votes, either in FPTP or in RCV-IRV.