UK ANCESTRY VISA OVERSTAY

A friend overstayed her Uk Ancestry VIsa by two years,She left unassisted voluntarily over five years ago to her country of birth,on departure at Heathrow the IO looked through her passport went away for a few minutes then handed her passport back saying 'one passport'..No overstayer stamp was entered to her passport nor was she given any paperwork.She assumed she would be on an overstayer watch list,but recently travelled to the Uk via Heathrow, on arrival she was given six months leave to enter and nothing was said of her previous overstay,while in the Uk she was reunited with close friends and was offered employment there,she stayed for two weeks and returned to her country of birth to apply for another Ancestry visa,on the application form it states she must include previous visits to the Uk in the last ten years which would prove that she overstayed,she is concerned that if she applies for the visa she will be refused due to her previous overstay,she was also convicted of drink driving during her overstay which was non custodial a fine and a driving ban which would now be spent as six years has passed,she regrets her actions and would like to return to the Uk to work settle and live,what are her chances of being successful? does the fact that she was recently allowed to enter as a visitor mean she will not be banned or did UKBA ever know she overstayed?she does not want to be banned after being able to visit recently.Any information on this subject would be greatly appreciated.

She needs to mention the overstay as otherwise she will be committing deception which attracts a 10 year ban on future applications for entry clearance.