The vocal ex-backbencher was on a campaign visit for the Conservatives in Cardiff.
She said every vote for minor parties takes Britain closer to a Labour-SNP coalition.
Labour said the Tory campaign in Wales has been "thoroughly negative" and "scaremongering".
"I have respect for minor parties and I do understand why some people are attracted to UKIP," said Ms Widdecombe.
"But the fact is that every vote that doesn't go to the Conservatives makes it more likely that we're going to end up with a Labour-SNP coalition."
Labour's Mari Williams responded: "Minister after minister has come to Wales, each neglecting to mention what the Tories' vision for Wales is, preferring instead to be critical and scaremonger.
"This isn't what people want to see and hear from their politicians."
Plaid Cymru's John Rowlands added: "People know that only Plaid Cymru can be trusted to work for Wales in Westminster to get parity of funding with Scotland and an end to Tory cuts."
Following the Welsh party leaders' final televised debate on Friday, the parties are all focusing on a final Bank Holiday weekend push to win over those still undecided ahead of next Thursday's vote.
While Labour is promising its "biggest organisational push" in the "most important election in a generation",  Plaid Cymru leader Leanne Wood is touring Arfon and Ynys Mon in the party's campaign bus in north Wales.
The Welsh Liberal Democrats have been pushing home their message for young people.
"We are passionate about creating a thriving, modern, fairer country in which every young person has the opportunity to succeed," said the party's Jenny Willott.
UKIP is spending Saturday hosting an action day in Bridgend.
The former shadow home secretary Ann Widdecombe says voters should ignore smaller parties and make a straight choice between the Tories and Labour.