Mrs Gillan was contacted within hours by various interest groups
The shadow Welsh secretary Cheryl Gillan has apologised and has promised to pay back £4.47 claimed for dog food as part of her parliamentary expenses.
The Tory MP for Chesham and Amersham told the BBC News Channel she was "absolutely mortified" by the claim.
Ms Gillan was one of the Conservatives named by the Daily Telegraph in the controversy over MP's expenses.
Conservative leader, David Cameron said the disclosures marked another bad day for Parliament.
Ms Gillan, who has been Shadow Welsh Secretary since December 2005, said the expense claim for dog food was a mistake and that both of her dogs had since died.
"I mistakenly submitted a food bill which contained items for which I did not intend to claim back. I am sorry for this and will immediately repay the amount," she said in a statement issued on Monday.
Cheryl Gillan said both of her dogs, including Curby, have died
The fees office also reduced two claims for gas bills because statements showed Ms Gillan's account was in credit.
She said this was because the gas company sent two bills containing duplicate information for a period of three months.
"This was identified by the fees office so the payment to me under the ACA (Additional Cost Allowance) was reduced accordingly."
Plans to set up an independent auditing body for claims are expected to be outlined on Monday, with Commons Speaker Michael Martin due to give a statement at 1530 BST.
The new body would be entirely independent and cost about £600,000 a year to run.
Millions of receipts backing up all MPs' expenses claims under the second homes allowance were due to be published in July after a long Freedom of Information campaign.
But details have been leaked to the Telegraph - which has been publishing selected excerpts over the last few days.
Gordon Brown has said "mistakes" were made by MPs in their use of Commons expenses.
The prime minister apologised on behalf of all political parties for some of the claims made and said public trust must be restored "immediately".
Plaid Cymru's Parliamentary leader added his voice to concerns.
Elfyn Llwyd MP told BBC Radio Cymru's Manylu programme it was "shameful" and said there were no excuses.
"What surprised me is that so much of it is going on," he said.
"We were aware of some stories about some individuals but dear me, it appears that every other one is at it. We have to re-examine the system from top to bottom."
Asked whether the public could be confident that Plaid Cymru MPs were spotless on the allowances issue, he said: "Yes, you have my word on that."