Full stop here. If this was a necessary action, then really, pushing for college scholarships and tippy top grades are probably the least of her concerns.
College will be there at any point. There is a college for every student. Some kids find great careers that don’t require a college education, believe it or not. Some kids take longer to travel this journey,
If you have taken over guardianship, there surely is a good reason for this to have happened, and likely it’s not a cheery one.
Is this a court ordered guardianship, or an unofficial agreement to care for this niece for the time being.