if angel was raised on pandora it means that she and jack lived as residential settlers during dahls occupation. grogmouth likely worked for the flynts who, being a high status family at the time, in turn worked for dahl.

baron flynt was the warden of thor, a dahl mining rig that doubled as a prison. the companys sole interest in pandora to begin with was to extract eridium and find alien relics, so a siren would be a priceless bargaining chip for their efforts.

all of this to say its very possible that the flynts were the ones who sent out the order for angel to be kidnapped.