[Wowfunhappy]

> To illustrate this -- try and gloss this sentence another way while conveying the meaning.

“Someone must have been watching her.”

I’m making some assumptions about the context of the sentence—but as long as you told me what the context was, I’m sure I could come up with an equally simple replacement.

Personally, I found the original sentence quite hard to parse, despite being a native speaker. It’s not good writing and a good editor would replace it.