The phrase "in the school" can mean "inside the school [building]." Last week there was a flood. There was a lot of damage in the fire station, but not much damage at all in the school. – J.R.♦Mar 28 '15 at 9:46 https://ell.stackexchange.com/questions/53712/in-what-contexts-can-i-say-in-the-school
Trying to say, it would be a very specific meaning, referring to the building as such, not the institution. Commonly, returning to school is understood as going back to school e.g. after a vacation. The institution would be meant, not specifically the school building.
Is Tini going back to school only in the physical sense?
English has another meaning for "going back to school": if a person has stopped attending school (stopped being educated in a school, for example to have a child or get a job) we say they "quit school" or "left school".
If they later decide to return to being educated in school, we say they "returned to school" or "went back to school." The language is exactly the same, but the meaning is quite different. Context is the only way we know which one is actually meant. It's also considered a very positive thing to "go back to school" in order to continue an interrupted education.