What is a word for giving an answer that's not incorrect, but leaves out a bunch of information? [duplicate]

Solution 1:

She is being laconic. Merriam-Webster:

: using or involving the use of a minimum of words : concise to the point of seeming rude or mysterious

The emphasis is on being terse or brief, using so few words that a lot of information might be left out.

"Willow decided she didn’t want to tell him that she was going to live with her dorky boyfriend, so she decided on something more laconic / she decided to give a more laconic answer"

Solution 2:

If you're OK with a word describing the purpose of her action, 'evasive' and 'equivocal' might work:

Merriam Webster defines evasive as:

: tending or intended to evade : equivocal
// evasive answers

and equivocal as:

: subject to two or more interpretations and usually used to mislead or confuse
// an equivocal statement

Otherwise, a simple option would be 'incomplete'.