The ex-wife sent a message to scold her mother-in-law. Can I sue her?

You can negotiate and mediate with them first.

If negotiation fails, you can choose to call the police. Whoever repeatedly sends insulting information and interferes with the normal life of others shall be detained for not more than five days or fined not more than 500 yuan. If the circumstances are serious, they shall be detained for more than 5 days 10 days, and may also be fined up to 500 yuan.

Insult and abuse others by sending text messages on mobile phones. If they don't infringe upon others' reputation in public, and they don't openly spread statements that are not conducive to others, and they can't prove that the behavior of sending text messages has reduced others' social recognition, then this person's behavior is immoral, but infringing on others' reputation is not in line with legal significance. Therefore, insulting or cursing others by sending short messages does not constitute a crime in the legal sense.