My general understanding is that people cannot be charged for simply for simply failing to inform the authorities of the criminal intents of others.
This could be due to the difficulty of establishing that somebody truly knew the other person's intent and a general judicial philosophy that citizens are not obligated to inform on other citizens.
Conspiracy charges seem to need the person having the same intent, and taking a direct step to facilitate that intent. Another possibility perhaps could Accessory before the fact. Maybe the prosecutor would not have to show same intent. Rather, awareness of the intent and a willingness to actively provide support.
Another possibility could be Accessory After the Fact type charges. I think, however, that would require that she actively hid or destroyed evidence.
Simply lying to the police, even regarding extremely serious crimes, seems to be either not chargeable, or very difficult to charge.