[shawxe]

> Essentially it means “it must have been the case that, at the moment we’re speaking of, someone was watching her.”

Another native English speaker here. This would be how I would parse "She had to have been being watched," but I think it's not quite the full picture in this sentence's case. It's important to note that the "would" adds the implication that this conclusion is being drawn based upon some other (possibly unspoken) observation or proposition.

I would say the meaning is probably closer to "In order for some unspoken condition to be true, it must also be true that, during the moment of time in the past about which we are speaking, someone was watching her."

[sfblah]

You’re right. I was doing it on my phone and forgot that word was even there.