Nikki's 45% or whatever it was in NH was impressive, but literally might be the highest she gets in any state. If the primaries were held before the Bragg indictment last year, a one-on-one race with Trump this early in the process would be almost definitionally competitive and winnable for a serious candidate. There's no shortage of Republicans who wanted to move on.
But Republicans saw the indictment as a political prosecution. They saw other indictments that seemed equally flimsy and politically motivated follow, attempts to remove him from ballots for a crime without charge or trial, remembered the government working with big tech to censor certain stories last time, all that stuff... and even many Republicans who really didn't like Trump all that much had their sense of fairness and justice triggered.
Even assuming they are right about many if not all of these indictments being political prosecutions, removal from the ballot being anti-democratic and skirting the norms of due process, government-directed censorship being anti-free speech and an instance of alphabet-agencies trying to pick winners and losers, all that... it still might not be rational to pick him over a better candidate. But people tend to vote emotionally, and the whole thing aroused sympathy and indignation and outright anger from plenty of people who would otherwise have voted for the generic "not Trump" candidate in the primary.
Nikki can rack up delegates, maybe 25-40% of them in most states for as long as she stays in. Maybe before the convention Trump will be in prison or prevented legally from being the nominee or have a heart attack or something, and she can leverage her delegates at convention. The GOP certainly needs a "Plan B" given reality. But I just don't see how she can beat Trump in the conventional sense or even get close in a post-Bragg primary.