PD does not even take the time to explain to Iona Grace why he is doing these things to her but if she was not such a dumb slut it would be obvious. He is having company later and she needs to be ready for them to use. If they want to hurt her she will need to be able to take the pain. If they want to use her holes she will need to be able to satisfy their desires. He is going to prepare her the only way he knows how. By using her just as brutally as his guests will.