Is talking to this person is in your job description? If not, block her, and why does she even have your number?

If talking to her is in your job description, then respond once a day at day time and then ignore the rest of the day. Certainly don’t respond at night.

If she texts in inappropriate times, just ignore. Turn notifications off.

We can’t control other people and there’s no way to know why she is this way. But you can control yourself. Just don’t respond