She turned half of England into a wasteland because it had been propped up for too long under policies that would have doomed (and were dooming) Great Britain. The mines and factories of the North of England were dragging Great Britain into destitution under the medieval belief that you should do the job that your father, your grandfather, and your great-grandfather did, because that's the way God intended it. Instead, she forced Northerners to seek better and more modern employment instead of protecting industries in which Great Britain could no longer compete. Yes, it was painful. But it was the smart thing to do and she did it with courage and without hesitation.
It's part of why I think President Obama's (theoretical) policy of pushing manufacturing in the US is simply stupid. Fine, support the manufacturing that makes sense in the US, but trying to restart the textile industry in the US, restarting large-scale manufacturing, etc., is just silly. Re-gear the nation for the post-industrial world, let Asia invest in the massive infrastructure of industrialization (and the US make money off of that by selling that infrastructure to Asia... or where do you think the prosperity of the 90s came from?) just before industrialization dies a long-delayed death, and be positioned for the next step while your global competitors are still taking the last step.
It's a gross over-simplification, but anyone who plays RTS games knows how it works. Against an AI or against a very green opponent, base building is the way to go. You build tough, layered defenses, invest resources in massive infrastructure, all for a small investment in flexible organic units. Advanced players go with a much higher percentage in those flexible organic units that allow a player to react to changing situations and to take advantage of them.
Big corporations are bad. They're inflexible. But government control is even worse. They're even more inflexible. Unions are bad. Unions, by definition, are against flexibility. A new piece of equipment that negates 3 union jobs and cuts the hours of the fourth? Evil. Never mind that it's what is best for the industry and society as a whole, and is in the long term interests of those 3 union laborers who'll get better jobs elsewhere if they are flexible enough to retool themselves.
Ask anyone who is a success what the most important point in their career was. For most, it's a "failure". It's getting fired from another job that they got comfortable with but they had outgrown. The trick is to 1.) Outgrow your old job, don't just sit there and suck up space, and 2.) Be ready for that next job that will challenge your growth.
Northerners got challenged by Thatcher's policies. Many of them are why Great Britain has done as well as it has for the last 30 years.