She wouldn't have. John Major became Prime Minister precisely because Maggie had become an electoral liability to the Conservatives.
I've always heard that the reason the Torys disposed of her was not because she was unpopular with the electorate, but had offending her party's rank-and-file with her anti-European Community messages.
What were Maggie's approval ratings 1989-1990?
I don't have approval info to hand, but the voting intention data really speaks for itself if you look at the difference between Tory support before and after that famous first ballot on the 20th November 1990.http://ukpollingreport.co.uk/historical-polls/voting-intention-1987-1992
Take ICM (traditionally, our most accurate pollster):
16th November 199049 37 9
And just a week later, 3 days after
Thatcher announces she'll go:46 40 10
Poll tax really damaged her (and the Tory brand in general for that matter) terminally.