I am not a teacher.
I would call "crying" an adjective modifying "her", pure and simple. I saw her green with envy. I saw her enraged. You saw a crying Matilda.
"Saw" cannot operate on "her" in a way that permits "crying" to be an object complement, and it is not copulative, either.
I can think of no objection to your view that "her crying" is a clause used as an object, though.
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