Trying to translate in French, I came up first with "Il eût fallu qu'elle eût été surveillée", but mostly because of morphological similarity (it's almost the same amount of verbs, right?). It's also just a more literary form of the simpler "Il aurait fallu qu'elle soit surveillée".
That being said, I have trouble to parse the original english sentence so I may be missing subtleties.
That being said, I have trouble to parse the original english sentence so I may be missing subtleties.