Example We don't say: "She's in room/lobby." We say:"She's in the room/lobby." So does the same rule not apply for "reception"?
"She is in the reception(area)." or Can we say:"She's in reception." and it would mean the same as "She's in the reception."?
You can say "She's in reception" or "She's at reception" to mean that she is in the reception area or at the reception desk. "She is at/in the reception" has a different meaning altogether.