Did Lesotho campaign against apartheid, keep silent? Was it economically reliant on South Africa? Was it under threat of being conquered? Did it collaborate with the South African government?
Great Question. Let me try and answer.
Did it collaborate? No. It really didn't. In literature like Andre Brink's A Dry White Season and in the biographies of resistance figures like Joe Slovo and Dennis Goldberg, Lesotho is mentioned as a favourite location for dissidents to flee from. The Lesotho government was tightly linked to the ANC and other "radical" African regimes like Mozambique and Libya.
Was it threatened by South Africa. No.
Although a lot of Apartheid South Africa can be inditenfied as fascists(at least by Paxton's definition), one thing South Africa was not was expansionist. Involvement in the Congo and Angola had more to do with Cold War politics than it did with Apartheid ideology and aspirations of regional hegemony.
Apartheid means seperation. Erich Louw's The Rise, Fall, and Legacy of Apartheid outlines the ideology of Apartheid the best. It was about creating a system in which white(read Afrikaans) supremacy and prosperity could be preserved and protected, while black South Africans could eventually set up their own independent states. Lesotho is many ways represents exactly what SA wanted to see. Independent black states, or using the Apartheid lexicon, bantustans. Hendrik Verwoerd himself expresses Apartheid as "neighborliness" and as "helping" black South Africa progress. And this is the belief of early Apartheid advocates as well. It is all about creating a reality where black and white are seperate.
Now in reality Apartheid was far more about preserving the cheap black labor that South Africa was built on, but that is the eternal argument of Apartheid, labour vs race.
The relation between the two states were horrible. Under President Jonathan (65-86) of Lesotho, he had thought he could talk sense into the Apartheid government/regime at first as the relation between himself and his contemporaries in the Apartheid state started off well.
Eventually he realized he could not, and he backed the ANC privately, then towards the 80s his advisors told him SA was going to collapse under the apartheid government due to its incompetence and failing economy. He then publicly came out and supported the ANC.
The Apartheid government demanded he route out the ANC, he refused, so they started to rig elections, and spread propaganda about him and then eventually sent in a force to remove him from power and installing their own puppet leader.
During Jonathan's time as president, the Apartheid government had backed numerous failed rebel groups to overthrow his government like the Lesotho Liberation Army as part of the Vakplaas operation. They eventually succeeded in corrupting a high ranking military member Justin Lekhanya who threw president Jonathan out of office and clamped down on the ANC and wink wink nudge nudge normalized relations with the apartheid government. By the time 1990s rolled around the Apartheid government had no use for him as it was on its way out, so he was removed by his handlers, another general installed as leader to pave the way for democracy again.
I think I can get to the core of your question which is why did SA an apartheid state permit for a black independent nation to exist in the middle of it. During colonialism the Boer and Brits tried to invade Lesotho who was a kingdom like the Zulus and Xhosas, etc. The only difference was as they were further inland, they had heard many terrible stories about the Europeans invading, pillaging, raping etc. the neighbouring states. This cause the Lesothans to try to desperately industrialize as fast as possible and buy up and develop the 3 main classes of weapons their African neighbours had not acquired or used in the manner they'd need to defend, machine guns, long range artillery and long range rifles. Lesotho got these and as such successfully repelled the European attacks and invasions, add on Lesotho as being very mountaneous, it was not easy to invade so the Brits just ended up signing a peace agreement with them.
By the time Apartheid rolled around in the 50s or so (you had different racist policies before then but they weren't called Apartheid), the Apartheid government had nothing to really gain from invading Lesotho. It wasn't a particularly large, rich or resource bound nation. They were busy invading the Congo, trying to stop Angola and Mozambqiue from getting independence or on their feet, they were tied up in Zimbabwe trying to support the Rhodesia regime and forces were spread thin via the "Frontline Wars".
" Did Lesotho campaign against apartheid, keep silent?"
Lesotho main prime minister during apartheid in SA had sought to work with them at first to end apartheid, them remove/overthrow them towards the end and came out as an open ANC supporter.
"Was it economically reliant on South Africa?"
To some extent, many of its people worked in mines in SA, which had stopped when the president came out and said he favoured ANC and Apartheid government shut the border.
"Was it under threat of being conquered?"
Not by SA during apartheid. In the 1800s Europeans in the regions launched several failed war attempts. Eventually the king requested the British enter a protectorate agreement to protect Lesotho and they had an agreement Lesotho pledge allegiance to the Brits and they'd save them from other European bullies in the region.
For SA to attempt a direct invasion/occupation for any prolonged period after that protectorate agreements ends in the 1960s, would have just made SA worse off on all fronts. They were bogged down in front line wars with other countries, it would hurt them diplomatically, it had no real reward except pushing the ANC rebels hiding their into other countries beyond the reach of SA intelligence. Much easier to track ANC in Lesotho than in Angola or Libya.
"Did it collaborate with the South African government?"
Under President Lekhanya, who was a SA Apartheid install/ puppet leader yes. However, by that point Apartheid was collapsing, the frontline wars were lost and Zimbabwe had gotten independence which was viewed as a total and utter defeat of the SA Apartheid dictatorship. They would go on to give Namibia independence because they realized they'd not win this conflict long term, so sought to divest of its tools/assets foreign. This left Lekhanya without support so he was removed, he outlived his purpose. Essentially, by the time SA got their collaborator in, there was no need for it anymore. They had lost every conflict they had been in across almost 10 different countries called the Frontline wars from 1960- late 1980s, they were surrounded by countries closing in and if they didn't transition to peaceful democracy they leaders of apartheid would probably get the Mussolini treatment.