She was positive that you had been dead for years now; so when you returned to the nation of Inazuma alive, she had a few choice words for you..

”You leave me for years, and now you decide to come back?” She spoke with a look of scorn on her face.

”Ei-? I can explain-” You tried to speak.

”You left like a coward.”

Ei was right - you had left so long ago, running away like the coward you are. You couldn’t deny it, but you thought she had forgiven you. Apparently not so much..