Duffy has pleaded not guilty to 31 charges of fraud, breach of trust and bribery related to expenses he claimed as a senator and later repaid with money from the prime minister's then chief of staff Nigel Wright. The trial, which began April 7 in the Ontario Court of Justice in Ottawa, is in its 30th day.
Scharf worked for Duffy for six months in 2011 while his full-time executive assistant Melanie Mercer was on maternity leave.
On Tuesday, Crown prosecutor Jason Neubauer had Scharf review a series of travel claims she had filled out for Duffy.
Scharf testified, as did Mercer before her, that Duffy had pre-signed blank travel claims for efficiency and expediency. But Scharf, who has worked in a number of parliamentary offices, including those of two prime ministers, said this was a common practice on Parliament Hill.
Scharf also testified that Duffy arranged to have the monthly fees of her cellphone paid through his associate Gerald Donohue after Senate administration said it would not cover the costs.
The court has heard that Donohue had been awarded a series of Senate research contracts with Duffy worth nearly $65,000.
The RCMP have said Donohue received the money for "little or no apparent work." Instead, the Crown alleges, that pool of money was used by Duffy, through Donohue, to pay for a series of expenses, some of which the Crown says would not have been covered by the Senate.
Duffy's defence lawyer Donald Bayne has argued that while it was "administratively irregular" to not have these expenses paid out through Senate finance, the action was not criminal.