If Becky ever came to trial, a lawyer might be able argue on her behalf that she's not capable of being fully responsible for her own actions. But I doubt Ilpholin really wants Becky being interrogated by Remnant, whether in court or not.
"We define a minor as one who has not reached the level of adult responsibility and independence set by their species and culture." Delisle says. Sakura and Brinika are about the same age, I think, but only one of them is considered a child.
"If there are factors that means a person should be considered as a unique entity, or separate from their typical species and culture, we do our best to take those into account. But most people come from a culture where there is a 'coming of age' ritual of some sort, whether it be an elaborate ceremony or something as simple as moving out of the parental home. In absence of any other considerations, that ritual is usually a sufficient marker for our purposes." In Emily's case, she's still in school and still lives with her mother.
Plus she cried and asked for her mother when she was giving her witness statement, but I imagine I'd do the same if I had narrowly escaped being abducted by Clarissa and Becky.