I found this reference on the tudorplace site - referring to the Thomas Howard affair:
Thomas was attainted by Act of parliament and sentenced to be executed; and, technically, lady Margaret was liable for the same punishment. Lord Thomas died in the Tower some months after. The poet Earl of Surrey recalls his uncle's in a poem. Commenting to the Emperor Carlos V on the severity of the measures, Ambassador Chapuys observed that Margaret was blameless, since in her case "copulation had not taken place". Even if it had, he went on drily, the "princess of Scotland" could scarcely be blamed, "seeing the number of domestic examples she has seen and sees daily".
I find it hard to believe that Chapuys really was so dim as to think she was a princess. I find it easier to believe that he was being humorous - which may have escaped Maria Perry (that book again)! Carlos V would have been familiar enough with the marital adventures of Margaret Tudor to know that her daughter was not a princess of Scotland. I can just hear him chortling about the story and Chapuys faux-naif narration!