She does. She may not be able to win a Democratic primary, but now that she's the nominee (or soon will be), she will be able to compete in a different field. Being unviable in a party's primary doesn't mean that they are necessarily unviable in the general.
Harris has basically hidden in a basement for the last four years. She's done nothing notable, but she's done nothing wrong either. This means that many attacks that have been sticking onto Biden are unlikely to stick onto her outside of general attacks (e.g., communist, socialist, woke, etc). Coming in this late, she has a chance to re-introduce herself to the nation again and change her image from four years ago, and she also has a limited time to really blunder. If she's going to be able to do that is a different question, but she has a good chance.
Her focus should be winning appeal the middle voters and try to match some of the concessions that Biden promises the Squad to shore up the flaky youth vote.