Not all people who live in trailers are "trailer trash", or even low income. In most of Florida, winters are quite mild, and a mobile home can be quite comfortable. There are many people who feel no need to have an expensive house and will live in a mobile home which allows them more resources for cars, boats, and vacations.
We do know that Anna had her own car and went to a private school, so the family doesn't appear to be too poor. We don't know, however, whether this car was for her own personal use. Possibly she was expected to provide a "taxi service" for her younger siblings and step-siblings.
I suspect the child custody hearings are more about child support payments than minor children leaving the country without both parents' consent.
We probably won't know much about family finances unless an arrest takes place. Defense lawyers are extremely expensive. if the family seeks a public defender for their minor child, financial information will become quite relevant. Even if well-off, I doubt Anna's grandparents would spend a dime for defense of someone charged with murdering their granddaughter.
There is just so much we don't know about this case. What were her stepbrother's demons? Why frequent school changes? Did stepbrother routinely crawl into Anna's bed in the middle of the night, or was this a one-time thing he did just to irritate her boyfriend? Or did her ex embellish the event? We know very little about Anna's life prior to this cruise, and even then, we only know snippets about what happened the night of her death.
Hopefully, these questions will be answered. It would not surprise me, however, if the perpetrator is found to be incompetent to stand trial and we may not get a full account.