This woman and her government regarded the Chilean dictator Pinochet (who murdered thousands) as a great friend, opposed sanctions against Apartheid South Africa, supported the Khmer Rouge and sold weapons to Saddam Hussein. Yes some great foreign policy decisions there 
...and laid the groundwork that ultimately crushed the pIRA's military movement and later forced it into the political power-sharing seen today, was instrumental in policies that forced the collapse of the Soviet Union, politically led of the sovereign defense of a British territory that could have simply been conveniently given up, and promoted the advancement of freedoms and liberty in the former Communist Bloc.
Every country was guilty of myopia concerning Latin America in the 80s and 90s; doesn't mean Thatcher should have been forgiven for it, but it puts her views in perspective (Pinochet also counted George Bush Sr among his friends). Saddam was funded and supplied with intel by several NATO countries for a multitude of reasons for quite some time (hint: Iran). Opposition to sanctions in South Africa were on the wrong side of history, I'll grant, and as for your claims about "supporting the Khmer Rouge," if you're referring to the UN backing of the Khmer Rouge by a number of Western governments, she certainly wasn't out of the ballpark of her contemporaries either. Black marks? Sure, but, when put in context, considerably less significant than her foreign policy successes,
I know there are some hardcore Thatcher-haters in the UK - you appear to count yourself among them - but she was quite well-respected for her foreign policy, and for good reason.