> too convoluted
It's a sentence that would typically be spoken rather than written, but it's only a step beyond "you would have had to have been there", which has genuine occurrences in Google Search.
https://www.google.com/search?q=%22You+would+have+had+to+hav...
Which is also funny, because it's apparently convoluted enough in English to have us regularly shorten it to "you had to be there" (which sounds correct, even though I'm fairly sure it's ungrammatical.
I would translate it as "debería haber estado vigilada". DeepL translate it as "tendría que haber sido vigilada". Both are much easier to understand.