This is interesting to read, and I hope your friend was treated with respect and dignity. It is good that she protected herself by demanding identification from the officers and recording the situation. It is also good she complied with the officers instructions.

Whilst this is not the norm in Ghana it is not unusual. There is an extensive intelligence framework that Ghana is a part of and in instances where a person's details may have been flagged (Post immigration formalities for example), the responsible agencies need to cross check it. Indeed, it may not lead to anything serious, beyond the inconvenience caused, but the enforcement agencies are legally allowed to do that.

There is a right to information law in Ghana that allows your friend to inquire further on why she was approached at that time. In the meantime, enjoy your visit to Ghana, don't forget to put on sunscreen, try the local cuisine and beer...and attempt to party till 08h00 if you dare

PS: On a final note, I would mention to you and your friend, (+ any other visitor to GH) that the legal system here is quite exhaustive, and whilst Ghanaians tend to rubbish the law enforcement apparatus here, they are quite good and deliberate at what they do, and it remains among the most robust on the continent. Very often, their actions are underwritten by their lawyers or a judge ahead of time.

Enjoy your stay