Eva knew Hazel was alive and well because she had been posting random pictures from her trip to France in their Discord chat. She was surprised the artist was bothering to contact her at all after the fight they had but she supposed this was Hazel's strange way of showing she cared about her feelings.
She knew Eva was deeply concerned about her safety. This was her way of letting her friend know she was okay without having to talk about what happened between them on the last day of her trip.
It was hard to believe that the man smiling so joyously next to Hazel at the top of the Eiffel Tower could possibly want to hurt her but still…
During their fight, she said that Eva could tell John Abramson that Billy Thornton wasn't a threat. But how would she explain knowing that without giving away her friend's secret? She was back and forth about it for weeks before finally daring to make the call.