Police prefer that criminal cases are resolved by compelling a confession. If a woman is told by the police they have her period data, most people would crack in that situation. Whether it holds up in court is mostly irrelevant.
It should go without saying, but never talk to police and if you’re being interviewed, insist on invoking your 6th amendment right to an attorney and your 5th amendment right to remain silent. And don’t engage with anything the police say.