Haley's communications team can put all the positive spin it wants on her massive defeats, but the writing is on the wall, and Trump is the inevitable GOP nominee. She hasn't won anything this campaign season, so there's no reason to believe she'd be able to defeat Biden. She should accept Trump's victory and get behind him so the party can be unified for the general election.
Haley has a large following — including with independents — and a different point of view from Trump. So she should stay in this race for however long she feels is necessary to put forth her opinions and show the Republican Party that Trump is the wrong choice. Continuing to run also keeps her in line to replace Trump should something unforeseen happen to the ex-president.