I think she probably has caught an infection leading to fever
and giddiness. Make sure she is able to take enough oral fluids.
If she had bone marrow transplant
recently, I think she may be on immunosuppressive medications like steroids
etc. These sort of medications reduce immunity significantly and they can easily catch an infection and infection can spread rapidly.
In this situation, it is advisable to contact your Hospital doctor and get her checked over in hospital. She may need some blood tests to rule out infection.
Dr Tejas Shah