Not necessarily. Sure, sanctions were a good idea, but foreign affairs are a whole load more complicated than that. It isn't always the best idea to have universal condemnation and sanctions.
Yeah sanctions and the general divide between the carrot and stick is a tough one. In hindsight successful sanctions look like courageous actions while failed ones look like a specific kind of barbarism that punishes people that have already been punished enough (global sanctions on Iraq and American sanctions on Cuba look especially stupid in a recent context). Likewise, knowing the right time to reach out to begin dialogue is tough--while Carter is viewed as a wimp, Nixon is celebrated for reaching out to China at the right time. Even during the Apartheid debate there were controversial actions... Paul Simon recorded Graceland in part to elevate black South African culture (in defiance of the boycott--not sanctions, of course, but still) and got a very divisive reception in South Africa for it.
I do think that Thatcher erred too far on the side of realism in FP and was too conservative, and I mean this in the Burkean sense, not just to mean she existed on the political right, in the sense that she valued order over liberty in several authoritarian cases that history has since declared to be immoral.
More generally to the thread's discussion...
I think jabs at Thatcher's foreign policy, or really jabs at any FP realism, are permissible but need to be contextualized with the above. Part of being a leader is that you're put in very hard situations that are deeply felt, and unlike your criticism, the blame is on you if you call it wrong long-term. C'est la vie. In opposing sanctions against South Africa (or in Russia's opposition of sanctions against iffy regimes today for much the same balance of geopolitical, fp realism, and stability reasons), she left herself open to the historical judgment that she was wrong, and that wrong was gravely immoral.
Finally, I think that celebrating the death of someone you don't like is an understandable human response, but something we should try to get past because it's rooted in a primal sort of need for vengeance or cosmic rebalancing, which I don't think is either helpful or enlightened. I mean, I understand it. It is what it is. But I try not to do it myself. The vast majority of people, even people who seem to be intolerably cruel, are generally trying to do this best. I really believe that most politicians of all stripes and across all history generally have a tough job and try to make the right calls. Some are able to, some are not. Some do more wrong than right, and some do wrong in part because their personality and experience leads them in the wrong direction.
I don't think Thatcher was a cartoonish villain, but nor do I accept that the supposedly incompetent, complacent, and decadent British left she aimed to reform or eradicate were; I think mostly people were trying their best, and some were better fits for their times and circumstances than others.
And all politicians of significant impact should get a state funeral regardless of legacy. It reflects the tremendous psychic impact they have on the body politic of the country, and the perk is the best kind because it can't be abused or corrupted. I'd hazard a guess that every PM who wins an election, every LO who serves more than a few years, and the odd Foreign / Finance secretaries should make the cut in most parliamentary countries.
Disclaimer: I live in Canada, my English father left the UK during Wilson or Callaghan, I'm old enough to have vague memories of the impacts of Reagan/Mulroney/Thatcher's neoliberal reforms on society but young enough that those were childish memories and I get the vast majority of my information from research and deep reading.