She, as most politicians, compete in a primary - that is where the real election is. Her district was going to vote for the Democrat candidate no matter who was selected in the primary. Lastly 57% may seem like a lot or whatever, but it's ~16,000 votes out of a potential ~700,000 for the district. Hell, 16k out of ~100,000 that voted last time isn't a huge amount.

REF: https://ballotpedia.org/New_York%27s_14th_Congressional_Dist...

But that's just a minor point, overall.