The opposition Democrat Party will tomorrow formally introduce Kingkan na Chiang Mai of as its candidate in the the Chiang Mai by-election.
Democrat executives picked Mrs Kingkan to stand in Constituency 3 in place of Kalayakorn Jiamkitwattana, who was earlier tipped to contest the April 21 poll.
The decision to switch candidates followed reports that those close to Ms Kalayakorn had set tough conditions for her to run under the Democrats' ticket, a source said.
One of the conditions was that Democrat leader Abhisit Vejjajiva meet her family in Chiang Mai, a party source said.
There was also an unresolved issue over the election campaign subsidy, which the party was asked to pay.
The Democrat Party said Mrs Kingkan, 65, has a clean record and enjoys good support in the constituency.
She will do battle with Pheu Thai candidate Yaowapa Wongsawat, the younger sister of ousted premier Thaksin Shinawatra.
Both are seeking to fill the seat vacated by Pheu Thai's Kasem Nimmonrat.
Democrat deputy leader Siriwan Pratsajaksatru, who oversees the party's election campaign in the North, has mobilised all Democrat MPs from all regions to support the campaign.
Mrs Kingkan defected from the dissolved Thai Rak Thai Party to the Democrats before the general election in 2007.