What does "she up to" mean?

[Keman]

Test No. errors/elem-7 "Prepositions", question 1

Say what you like but I simply don't understand what she's over to - it just doesn't make sense.

(a) but
(b) over to
(c) make sense

Test No. errors/elem-7 "Prepositions", answer 1

Say what you like but I simply don't understand what she's up to - it just doesn't make sense.

Correct entry: up to
The error was: (b) over to
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I DID NOT UNDERSTAND THE QUESTION

Keman

[Alan]

This means I don't know what she's doing in the sense that I believe she's doing something strange and it doesn't seem to be normal.
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English as a Second Language
You can read my ESL story Present Simple

[Lost_Soul]

Hi!

Maybe, on about is aslo a possible option, because I kind of know that to be on about = be talking about.
Do you find my reasoning plausible?

[Conchita]