Ingrid was a bully. During my career as a civil rights attorney, I stood up to many bullies on behalf of their victims (my clients).
The thing I know to be true about bullies is that they operate from a lack of self-confidence, feeling unloved and/or not valued, and, often, a deep sense of self-loathing. They are usually people who have been deeply hurt and they act out against others in an attempt to feel better about themselves. A successfuly bully often gets drunk with power and gradually becomes increasingly abusive until someone or something stops them.
And that describes Ingrid, doesn't it? She was an orphan, who undoubtedly felt unloved and unwanted, living in a place where she believed power mattered a great deal. And she wanted to get something that Fenna had -- lovely boots, real friendship, the respect of the other orphans -- but lacked the skills and/or intellect to obtain them without abusing Fenna. She was really a tragic character because I wanted to sit her down, explain her behavior to her, and help her see that she could overcome her circumstances without resorting to mistreating others.
I have had the experience of being accused of doing something I did not do, and it is excruciatingly painful and frustrating. I recall one incident that made me particularly angry because the accuser knew me well enough that there never should have been such an accusation. It revealed the toxic nature of a relationship that had to end, so it all worked out in my favor, as everything eventually does because karma is real.