I guess it depends on the system that your sister's TA use, if it is a big TA business such as STA, it would be possible to use any of the above links to check your reservation.
But if your sister booked it through the local TA and the system used to book is non- Amdeus, Sabre or Galileo (such as my usual TA), it would be difficult to trace reservations AFAIK. (My MEL-HKG-MEL is booked through the Abacus system, a booking tool for small-scale TA), so check with your sister to see which system her TA booked it on.