WASHINGTON — On the April night she answered a 1 a.m. phone call instructing her to take the next plane back to Washington, Marie L. Yovanovitch, the ousted United States ambassador to Ukraine, was at her home in Kiev — after having just finished hosting an event to honor a young anticorruption activist who had been killed in horrific fashion.

The activist, Kateryna Handziuk, was outside her home in the Ukrainian city of Kherson in July 2018 when someone splashed her with a quart of sulfuric acid, severely burning more than 30 percent of her body. After 11 surgeries over three months, Ms. Handziuk succumbed to her excruciating wounds. She was 33.

In public impeachment hearings, the former ambassador testified Friday about the chronology of her abrupt recall from Ukraine after a campaign of unsubstantiated allegations against her that reached President Trump. Speaking before a House committee, she also spotlighted Ms. Handziuk’s story, and underscored why she had been honoring her legacy that April night in an official award ceremony attended by Ms. Handziuk’s father.