I am Maarten a Singapore PR from the Netherlands who works and lives in Singapore

A few months ago I invited a lady from the Philippines for a social visit to Singapore but when entering she was refused entry by Singapore customs. And was treated as a criminal before being send back to Singapore.
Because I am a PR it was possible for me to appeal against the refused entry of her. Yesterday after waiting for 9 weeks I received the information that the appeal was rejected.
The rejection letter did not give any information on the reason why, further they did not give any information how to pursue further.
The current situation is highly frustrating since she just wants to come to Singapore to visit me ... for a week or so .. what is the big deal??
I dont want to give up yet ... she is a great person and it would be unacceptable for me that she is simply not welcome to Singapore.
Could anyone be so kind to suggest me what to do next? I am totally in the dark

Your help is very much appreciated

Cheers,
Maarten