OP.
The objection would have to be based on strong planning ground such as overlooking, loss of privacy, loss of sunlight, augmentation to boundaries, affects on services and infrastructure etc. If none of the above are being affected in a significant way its unlikely that the council will require significant changes to the development.
What would happening if an objection is submitted is:
1. a visit from the Local Authority enforcement officer to establish if the development is unauthorised
2. if deemed unauthorised, a letter of enforcement will be sent requiring the works to cease and an application to be made in order to authorise the work.
3. a planning application for retention and completion will ensue.
4. during this your relative can make his/her case
5. a decision will then be made by the council
6. an objectee then has the option to bring the case to An Bord Pleanala.
7. once BP decides, case closed (pretty much)