Witness for divorce case.

Its upto you, if you dont feel to go in the court as a witness then no one can compell you to appear as a witness. Dont be afraid of her threats. Let her do whatever she wants to do. She wont come to your home and threathen your family. Next time if she tries to threat you then you can warn her that you will file police complaint against her in local police station.

Bt she has mentioned that she will send me a legal notice to appear in court and give witness for her so that her case becomes strong

You can refuse to accept her request to let in evidence against her husband in the divorce  case.

If she is trying to send summons through court, you wait and watch for it, it is not very  much necessary that you have to attend the court to let in evidence as a witness. 

You cannot be forced to give evidence in court against your willingness in a case which is totally unrelated to you. 

In fact the court will not entertain her applicaiton to summon you even if she is adding you as a witness in the list of witnesses. 

But then she is saying she has all the chats and she will send me legal notice and if I don't accept the court notice den there will a problem for me. She also mentioned she will go through the legal procedure. So is there any changes that she can send me notice and should i worry abt this?

You can ignore her threats.

If she is sending any legal notice from her side, you engage the services of a lawyer and issue a fitting reply denying her allegations.

The court will not entertain her petition to summon you as witness because there's no relevance to the case proceedings.

You can consult a lawyer and be apprised of further issues and steps to be taken to defend your interests.