The game doesn't care. If she "knows" the answer, then she must tell that answer to the caster. That is what the mechanics demand. If you avoid giving the answer that she "knows", you are either cheating or house ruling the mechanics away.
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The mechanics demand the truth that she "knows", so she has to give it. You don't get to change that mechanic by introducing more fluff. At least not without a house rule.
This is a bit weird for two reasons.
First, there are strange category errors.
Games aren't the sorts of things that care (or fail to care). And the mechanics demand nothing of any character: mechanics are things that exist and operate in the real world, and demand things of the players.
In this particular case, the mechanics demand that the the player hand over certain information - broadly, the information to which his/her PC has a canonical form of access. A peculiarity of ZoT is that it is a
disadvantage to be subject to that spell if your PC has a high INT and/or you are an informed player. Luckily for the player of the 5 INT character, the PC has a low INT and the player is not well informed!
The second weird thing is that you think it is some sort of "touche" event to point out that this is a non-standard application of the ZoT spell ("house rule"). Of course it is (and I don't think [MENTION=6801328]Elfcrusher[/MENTION] has denied that). If you're going to do funky things with the INT score, of course information-gathering/disclosure-forcing spells are going to generate some corner cases.
To bring up a comparison: in the Marvel Heroic RP game, the following characters all have a high Durability score: Captain American, Invisible Woman and The Thing. For Cap it is his shield; for Sue Storm her forcefield; for Ben Grimm his skin.
That means that these Durability scores can be circumvented in different ways: for instance, if The Thing is unconscious he is still durable, whereas that is not so for Captain America or Invisible Woman - in mechanical terms, if one of these characters is unconscious than his/her player can't declare an action that draws upon the Durability stat.
The game is not
broken because it uses the same stat to represent much the same outcome (in typical circumstances these characters can't easily be hurt) although, in the fiction, the reason for being hard to hurt is quite different. It demands paying attention to the fiction, especially as we move towards edge cases, but that's a virtue in a RPG (isn't it?).
[MENTION=6801328]Elfcrusher[/MENTION] is presenting INT, and ZoT, in much the same way. And it has much the same consequences - some more marginal or atypical cases require closer attention to the fiction in order to establish a clear narration.