I'm reporting you two for madness
Penny Carter was a journalist, working as science correspondent for The Observer. She attended a press conference at Adipose Industries. She was very sceptical about the diet pill, and decided to investigate it a bit further. She stayed at Adipose Industries till after closing time, hidden in a toilet stall. She was discovered by Miss Foster, thus saving Donna who was hiding in a stall near by.
Miss Foster took Penny to an office, and her security men tied her into a chair. She was later released by the Doctor and warned to get out, but stays behind to collect files and ends up getting tied up again. When Miss Foster sets the Inducer, she tells Penny to mark the date, happy birthday. After the March of the Adipose, Penny escapes and then tells the Doctor and Donna Noble that she will report them for madness. (DW: Partners in Crime)
Behind the Scenes
According to The Writer's Tale, before Catherine Tate agreed to reprise her role as Donna Noble, Russell T Davies wrote a character called Penny Carter to be the Doctor's new companion beginning with Partners in Crime. This character was scrapped when Tate agreed to appear as Donna. Penny Carter was later used as the name of an investigative journalist who was investigating Adipose Industries. In his early notes regarding the character of Penny (reproduced in The Writer's Tale), Davies described her as being in her 30s and Donna Noble-esque.